Appendix A. Contributed Scripts
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2023-12-01
These scripts, while not fitting into the text of this document, doillustrate some interesting shell programming techniques. They are useful,too. Have fun analyzing and running them.
Example A-1. mailformat: Formatting an e-mail message
1 #!/bin/bash 2 # mail-format.sh (ver. 1.1): Format e-mail messages. 3 4 # Gets rid of carets, tabs, and also folds excessively long lines. 5 6 # ================================================================= 7 # Standard Check for Script Argument(s) 8 ARGS=1 9 E_BADARGS=65 10 E_NOFILE=66 11 12 if [ $# -ne $ARGS ] # Correct number of arguments passed to script? 13 then 14 echo "Usage: `basename $0` filename" 15 exit $E_BADARGS 16 fi 17 18 if [ -f "$1" ] # Check if file exists. 19 then 20 file_name=$1 21 else 22 echo "File \"$1\" does not exist." 23 exit $E_NOFILE 24 fi 25 # ================================================================= 26 27 MAXWIDTH=70 # Width to fold excessively long lines to. 28 29 # --------------------------------- 30 # A variable can hold a sed script. 31 sedscript='s/^>// 32 s/^ *>// 33 s/^ *// 34 s/ *//' 35 # --------------------------------- 36 37 # Delete carets and tabs at beginning of lines, 38 #+ then fold lines to $MAXWIDTH characters. 39 sed "$sedscript" $1 | fold -s --width=$MAXWIDTH 40 # -s option to "fold" 41 #+ breaks lines at whitespace, if possible. 42 43 44 # This script was inspired by an article in a well-known trade journal 45 #+ extolling a 164K MS Windows utility with similar functionality. 46 # 47 # An nice set of text processing utilities and an efficient 48 #+ scripting language provide an alternative to bloated executables. 49 50 exit 0
Example A-2. rn: A simple-minded file rename utility
This script is a modification of Example 12-19.
1 #! /bin/bash 2 # 3 # Very simpleminded filename "rename" utility (based on "lowercase.sh"). 4 # 5 # The "ren" utility, by Vladimir Lanin (lanin@csd2.nyu.edu), 6 #+ does a much better job of this. 7 8 9 ARGS=2 10 E_BADARGS=65 11 ONE=1 # For getting singular/plural right (see below). 12 13 if [ $# -ne "$ARGS" ] 14 then 15 echo "Usage: `basename $0` old-pattern new-pattern" 16 # As in "rn gif jpg", which renames all gif files in working directory to jpg. 17 exit $E_BADARGS 18 fi 19 20 number=0 # Keeps track of how many files actually renamed. 21 22 23 for filename in *$1* #Traverse all matching files in directory. 24 do 25 if [ -f "$filename" ] # If finds match... 26 then 27 fname=`basename $filename` # Strip off path. 28 n=`echo $fname | sed -e "s/$1/$2/"` # Substitute new for old in filename. 29 mv $fname $n # Rename. 30 let "number += 1" 31 fi 32 done 33 34 if [ "$number" -eq "$ONE" ] # For correct grammar. 35 then 36 echo "$number file renamed." 37 else 38 echo "$number files renamed." 39 fi 40 41 exit 0 42 43 44 # Exercises: 45 # --------- 46 # What type of files will this not work on? 47 # How can this be fixed? 48 # 49 # Rewrite this script to process all the files in a directory 50 #+ containing spaces in their names, and to rename them, 51 #+ substituting an underscore for each space.
Example A-3. blank-rename: renames filenames containingblanks
This is an even simpler-minded version of previous script.
1 #! /bin/bash 2 # blank-rename.sh 3 # 4 # Substitutes underscores for blanks in all the filenames in a directory. 5 6 ONE=1 # For getting singular/plural right (see below). 7 number=0 # Keeps track of how many files actually renamed. 8 FOUND=0 # Successful return value. 9 10 for filename in * #Traverse all files in directory. 11 do 12 echo "$filename" | grep -q " " # Check whether filename 13 if [ $? -eq $FOUND ] #+ contains space(s). 14 then 15 fname=$filename # Strip off path. 16 n=`echo $fname | sed -e "s/ /_/g"` # Substitute underscore for blank. 17 mv "$fname" "$n" # Do the actual renaming. 18 let "number += 1" 19 fi 20 done 21 22 if [ "$number" -eq "$ONE" ] # For correct grammar. 23 then 24 echo "$number file renamed." 25 else 26 echo "$number files renamed." 27 fi 28 29 exit 0
Example A-4. encryptedpw: Uploading to an ftp site,using a locally encrypted password
1 #!/bin/bash 2 3 # Example "ex72.sh" modified to use encrypted password. 4 5 # Note that this is still rather insecure, 6 #+ since the decrypted password is sent in the clear. 7 # Use something like "ssh" if this is a concern. 8 9 E_BADARGS=65 10 11 if [ -z "$1" ] 12 then 13 echo "Usage: `basename $0` filename" 14 exit $E_BADARGS 15 fi 16 17 Username=bozo # Change to suit. 18 pword=/home/bozo/secret/password_encrypted.file 19 # File containing encrypted password. 20 21 Filename=`basename $1` # Strips pathname out of file name. 22 23 Server="XXX" 24 Directory="YYY" # Change above to actual server name & directory. 25 26 27 Password=`cruft <$pword` # Decrypt password. 28 # Uses the author's own "cruft" file encryption package, 29 #+ based on the classic "onetime pad" algorithm, 30 #+ and obtainable from: 31 #+ Primary-site: ftp://ibiblio.org/pub/Linux/utils/file 32 #+ cruft-0.2.tar.gz [16k] 33 34 35 ftp -n $Server <<End-Of-Session 36 user $Username $Password 37 binary 38 bell 39 cd $Directory 40 put $Filename 41 bye 42 End-Of-Session 43 # -n option to "ftp" disables auto-logon. 44 # Note that "bell" rings 'bell' after each file transfer. 45 46 exit 0
Example A-5. copy-cd: Copying a data CD
1 #!/bin/bash 2 # copy-cd.sh: copying a data CD 3 4 CDROM=/dev/cdrom # CD ROM device 5 OF=/home/bozo/projects/cdimage.iso # output file 6 # /xxxx/xxxxxxx/ Change to suit your system. 7 BLOCKSIZE=2048 8 SPEED=2 # May use higher speed if supported. 9 DEVICE=cdrom 10 # DEVICE="0,0" on older versions of cdrecord. 11 12 echo; echo "Insert source CD, but do *not* mount it." 13 echo "Press ENTER when ready. " 14 read ready # Wait for input, $ready not used. 15 16 echo; echo "Copying the source CD to $OF." 17 echo "This may take a while. Please be patient." 18 19 dd if=$CDROM of=$OF bs=$BLOCKSIZE # Raw device copy. 20 21 22 echo; echo "Remove data CD." 23 echo "Insert blank CDR." 24 echo "Press ENTER when ready. " 25 read ready # Wait for input, $ready not used. 26 27 echo "Copying $OF to CDR." 28 29 cdrecord -v -isosize speed=$SPEED dev=$DEVICE $OF 30 # Uses Joerg Schilling's "cdrecord" package (see its docs). 31 # http://www.fokus.gmd.de/nthp/employees/schilling/cdrecord.html 32 33 34 echo; echo "Done copying $OF to CDR on device $CDROM." 35 36 echo "Do you want to erase the image file (y/n)? " # Probably a huge file. 37 read answer 38 39 case "$answer" in 40 [yY]) rm -f $OF 41 echo "$OF erased." 42 ;; 43 *) echo "$OF not erased.";; 44 esac 45 46 echo 47 48 # Exercise: 49 # Change the above "case" statement to also accept "yes" and "Yes" as input. 50 51 exit 0
Example A-6. Collatz series
1 #!/bin/bash
2 # collatz.sh
3
4 # The notorious "hailstone" or Collatz series.
5 # -------------------------------------------
6 # 1) Get the integer "seed" from the command line.
7 # 2) NUMBER <--- seed
8 # 3) Print NUMBER.
9 # 4) If NUMBER is even, divide by 2, or
10 # 5)+ if odd, multiply by 3 and add 1.
11 # 6) NUMBER <--- result
12 # 7) Loop back to step 3 (for specified number of iterations).
13 #
14 # The theory is that every sequence,
15 #+ no matter how large the initial value,
16 #+ eventually settles down to repeating "4,2,1..." cycles,
17 #+ even after fluctuating through a wide range of values.
18 #
19 # This is an instance of an "iterate",
20 #+ an operation that feeds its output back into the input.
21 # Sometimes the result is a "chaotic" series.
22
23
24 MAX_ITERATIONS=200
25 # For large seed numbers (>32000), increase MAX_ITERATIONS.
26
27 h=${1:-$$} # Seed
28 # Use $PID as seed,
29 #+ if not specified as command-line arg.
30
31 echo
32 echo "C($h) --- $MAX_ITERATIONS Iterations"
33 echo
34
35 for ((i=1; i<=MAX_ITERATIONS; i++))
36 do
37
38 echo -n "$h "
39 # ^^^^^
40 # tab
41
42 let "remainder = h % 2"
43 if [ "$remainder" -eq 0 ] # Even?
44 then
45 let "h /= 2" # Divide by 2.
46 else
47 let "h = h*3 + 1" # Multiply by 3 and add 1.
48 fi
49
50
51 COLUMNS=10 # Output 10 values per line.
52 let "line_break = i % $COLUMNS"
53 if [ "$line_break" -eq 0 ]
54 then
55 echo
56 fi
57
58 done
59
60 echo
61
62 # For more information on this mathematical function,
63 #+ see "Computers, Pattern, Chaos, and Beauty", by Pickover, p. 185 ff.,
64 #+ as listed in the bibliography.
65
66 exit 0Example A-7. days-between: Calculate number of daysbetween two dates
1 #!/bin/bash
2 # days-between.sh: Number of days between two dates.
3 # Usage: ./days-between.sh [M]M/[D]D/YYYY [M]M/[D]D/YYYY
4 #
5 # Note: Script modified to account for changes in Bash 2.05b
6 #+ that closed the loophole permitting large negative
7 #+ integer return values.
8
9 ARGS=2 # Two command line parameters expected.
10 E_PARAM_ERR=65 # Param error.
11
12 REFYR=1600 # Reference year.
13 CENTURY=100
14 DIY=365
15 ADJ_DIY=367 # Adjusted for leap year + fraction.
16 MIY=12
17 DIM=31
18 LEAPCYCLE=4
19
20 MAXRETVAL=255 # Largest permissable
21 #+ positive return value from a function.
22
23 diff= # Declare global variable for date difference.
24 value= # Declare global variable for absolute value.
25 day= # Declare globals for day, month, year.
26 month=
27 year=
28
29
30 Param_Error () # Command line parameters wrong.
31 {
32 echo "Usage: `basename $0` [M]M/[D]D/YYYY [M]M/[D]D/YYYY"
33 echo " (date must be after 1/3/1600)"
34 exit $E_PARAM_ERR
35 }
36
37
38 Parse_Date () # Parse date from command line params.
39 {
40 month=${1%%/**}
41 dm=${1%/**} # Day and month.
42 day=${dm#*/}
43 let "year = `basename $1`" # Not a filename, but works just the same.
44 }
45
46
47 check_date () # Checks for invalid date(s) passed.
48 {
49 [ "$day" -gt "$DIM" ] || [ "$month" -gt "$MIY" ] || [ "$year" -lt "$REFYR" ] && Param_Error
50 # Exit script on bad value(s).
51 # Uses "or-list / and-list".
52 #
53 # Exercise: Implement more rigorous date checking.
54 }
55
56
57 strip_leading_zero () # Better to strip possible leading zero(s)
58 { #+ from day and/or month
59 return ${1#0} #+ since otherwise Bash will interpret them
60 } #+ as octal VALUES (NULL, sect 2.9.2.1).
61
62
63 day_index () # Gauss' Formula:
64 { # Days from Jan. 3, 1600 to date passed as param.
65
66 day=$1
67 month=$2
68 year=$3
69
70 let "month = $month - 2"
71 if [ "$month" -le 0 ]
72 then
73 let "month += 12"
74 let "year -= 1"
75 fi
76
77 let "year -= $REFYR"
78 let "indexyr = $year / $CENTURY"
79
80
81 let "Days = $DIY*$year + $year/$LEAPCYCLE - $indexyr + $indexyr/$LEAPCYCLE + $ADJ_DIY*$month/$MIY + $day - $DIM"
82 # For an in-depth explanation of this algorithm, see
83 #+ http://home.t-online.de/home/berndt.schwerdtfeger/cal.htm
84
85
86 echo $Days
87
88 }
89
90
91 calculate_difference () # Difference between to day indices.
92 {
93 let "diff = $1 - $2" # Global variable.
94 }
95
96
97 abs () # Absolute value
98 { # Uses global "value" variable.
99 if [ "$1" -lt 0 ] # If negative
100 then #+ then
101 let "value = 0 - $1" #+ change sign,
102 else #+ else
103 let "value = $1" #+ leave it alone.
104 fi
105 }
106
107
108
109 if [ $# -ne "$ARGS" ] # Require two command line params.
110 then
111 Param_Error
112 fi
113
114 Parse_Date $1
115 check_date $day $month $year # See if valid date.
116
117 strip_leading_zero $day # Remove any leading zeroes
118 day=$? #+ on day and/or month.
119 strip_leading_zero $month
120 month=$?
121
122 let "date1 = `day_index $day $month $year`"
123
124
125 Parse_Date $2
126 check_date $day $month $year
127
128 strip_leading_zero $day
129 day=$?
130 strip_leading_zero $month
131 month=$?
132
133 date2=$(day_index $day $month $year) # Command substitution.
134
135
136 calculate_difference $date1 $date2
137
138 abs $diff # Make sure it's positive.
139 diff=$value
140
141 echo $diff
142
143 exit 0
144 # Compare this script with
145 #+ the implementation of Gauss' Formula in a C program at:
146 #+ http://buschencrew.hypermart.net/software/datedifExample A-8. Make a "dictionary"
1 #!/bin/bash 2 # makedict.sh [make dictionary] 3 4 # Modification of /usr/sbin/mkdict script. 5 # Original script copyright 1993, by Alec Muffett. 6 # 7 # This modified script included in this document in a manner 8 #+ consistent with the "LICENSE" document of the "Crack" package 9 #+ that the original script is a part of. 10 11 # This script processes text files to produce a sorted list 12 #+ of words found in the files. 13 # This may be useful for compiling dictionaries 14 #+ and for lexicographic research. 15 16 17 E_BADARGS=65 18 19 if [ ! -r "$1" ] # Need at least one 20 then #+ valid file argument. 21 echo "Usage: $0 files-to-process" 22 exit $E_BADARGS 23 fi 24 25 26 # SORT="sort" # No longer necessary to define options 27 #+ to sort. Changed from original script. 28 29 cat $* | # Contents of specified files to stdout. 30 tr A-Z a-z | # Convert to lowercase. 31 tr ' ' '\012' | # New: change spaces to newlines. 32 # tr -cd '\012[a-z][0-9]' | # Get rid of everything non-alphanumeric 33 #+ (original script). 34 tr -c '\012a-z' '\012' | # Rather than deleting 35 #+ now change non-alpha to newlines. 36 sort | # $SORT options unnecessary now. 37 uniq | # Remove duplicates. 38 grep -v '^#' | # Delete lines beginning with a hashmark. 39 grep -v '^$' # Delete blank lines. 40 41 exit 0
Example A-9. Soundex conversion
1 #!/bin/bash
2 # soundex.sh: Calculate "soundex" code for names
3
4 # =======================================================
5 # Soundex script
6 # by
7 # Mendel Cooper
8 # thegrendel@theriver.com
9 # 23 January, 2002
10 #
11 # Placed in the Public Domain.
12 #
13 # A slightly different version of this script appeared in
14 #+ Ed Schaefer's July, 2002 "Shell Corner" column
15 #+ in "Unix Review" on-line,
16 #+ http://www.unixreview.com/documents/uni1026336632258/
17 # =======================================================
18
19
20 ARGCOUNT=1 # Need name as argument.
21 E_WRONGARGS=70
22
23 if [ $# -ne "$ARGCOUNT" ]
24 then
25 echo "Usage: `basename $0` name"
26 exit $E_WRONGARGS
27 fi
28
29
30 assign_value () # Assigns numerical value
31 { #+ to letters of name.
32
33 val1=bfpv # 'b,f,p,v' = 1
34 val2=cgjkqsxz # 'c,g,j,k,q,s,x,z' = 2
35 val3=dt # etc.
36 val4=l
37 val5=mn
38 val6=r
39
40 # Exceptionally clever use of 'tr' follows.
41 # Try to figure out what is going on here.
42
43 value=$( echo "$1" \
44 | tr -d wh \
45 | tr $val1 1 | tr $val2 2 | tr $val3 3 \
46 | tr $val4 4 | tr $val5 5 | tr $val6 6 \
47 | tr -s 123456 \
48 | tr -d aeiouy )
49
50 # Assign letter values.
51 # Remove duplicate numbers, except when separated by vowels.
52 # Ignore vowels, except as separators, so delete them last.
53 # Ignore 'w' and 'h', even as separators, so delete them first.
54 #
55 # The above command substitution lays more pipe than a plumber <g>.
56
57 }
58
59
60 input_name="$1"
61 echo
62 echo "Name = $input_name"
63
64
65 # Change all characters of name input to lowercase.
66 # ------------------------------------------------
67 name=$( echo $input_name | tr A-Z a-z )
68 # ------------------------------------------------
69 # Just in case argument to script is mixed case.
70
71
72 # Prefix of soundex code: first letter of name.
73 # --------------------------------------------
74
75
76 char_pos=0 # Initialize character position.
77 prefix0=${name:$char_pos:1}
78 prefix=`echo $prefix0 | tr a-z A-Z`
79 # Uppercase 1st letter of soundex.
80
81 let "char_pos += 1" # Bump character position to 2nd letter of name.
82 name1=${name:$char_pos}
83
84
85 # ++++++++++++++++++++++++++ Exception Patch +++++++++++++++++++++++++++++++++
86 # Now, we run both the input name and the name shifted one char to the right
87 #+ through the value-assigning function.
88 # If we get the same value out, that means that the first two characters
89 #+ of the name have the same value assigned, and that one should cancel.
90 # However, we also need to test whether the first letter of the name
91 #+ is a vowel or 'w' or 'h', because otherwise this would bollix things up.
92
93 char1=`echo $prefix | tr A-Z a-z` # First letter of name, lowercased.
94
95 assign_value $name
96 s1=$value
97 assign_value $name1
98 s2=$value
99 assign_value $char1
100 s3=$value
101 s3=9$s3 # If first letter of name is a vowel
102 #+ or 'w' or 'h',
103 #+ then its "value" will be null (unset).
104 #+ Therefore, set it to 9, an otherwise
105 #+ unused value, which can be tested for.
106
107
108 if [[ "$s1" -ne "$s2" || "$s3" -eq 9 ]]
109 then
110 suffix=$s2
111 else
112 suffix=${s2:$char_pos}
113 fi
114 # ++++++++++++++++++++++ end Exception Patch +++++++++++++++++++++++++++++++++
115
116
117 padding=000 # Use at most 3 zeroes to pad.
118
119
120 soun=$prefix$suffix$padding # Pad with zeroes.
121
122 MAXLEN=4 # Truncate to maximum of 4 chars.
123 soundex=${soun:0:$MAXLEN}
124
125 echo "Soundex = $soundex"
126
127 echo
128
129 # The soundex code is a method of indexing and classifying names
130 #+ by grouping together the ones that sound alike.
131 # The soundex code for a given name is the first letter of the name,
132 #+ followed by a calculated three-number code.
133 # Similar sounding names should have almost the same soundex codes.
134
135 # Examples:
136 # Smith and Smythe both have a "S-530" soundex.
137 # Harrison = H-625
138 # Hargison = H-622
139 # Harriman = H-655
140
141 # This works out fairly well in practice, but there are numerous anomalies.
142 #
143 #
144 # The U.S. Census and certain other governmental agencies use soundex,
145 # as do genealogical researchers.
146 #
147 # For more information,
148 #+ see the "National Archives and Records Administration home page",
149 #+ http://www.nara.gov/genealogy/soundex/soundex.html
150
151
152
153 # Exercise:
154 # --------
155 # Simplify the "Exception Patch" section of this script.
156
157 exit 0Example A-10. "Game of Life"
https://www.xnip.cn/wp-content/uploads/2022/11/Example-A-10.txt
Example A-11. Data file for "Game of Life"
1 # This is an example "generation 0" start-up file for "life.sh". 2 # -------------------------------------------------------------- 3 # The "gen0" file is a 10 x 10 grid using a period (.) for live cells, 4 #+ and an underscore (_) for dead ones. We cannot simply use spaces 5 #+ for dead cells in this file because of a peculiarity in Bash arrays. 6 # [Exercise for the reader: explain this.] 7 # 8 # Lines beginning with a '#' are comments, and the script ignores them. 9 __.__..___ 10 ___._.____ 11 ____.___.. 12 _._______. 13 ____._____ 14 ..__...___ 15 ____._____ 16 ___...____ 17 __.._..___ 18 _..___..__
+++
The following two scripts are by Mark Moraes of the Universityof Toronto. See the enclosed file "Moraes-COPYRIGHT"for permissions and restrictions.
Example A-12. behead: Removing mail and news message headers
1 #! /bin/sh 2 # Strips off the header from a mail/News message i.e. till the first 3 # empty line 4 # Mark Moraes, University of Toronto 5 6 # ==> These comments added by author of this document. 7 8 if [ $# -eq 0 ]; then 9 # ==> If no command line args present, then works on file redirected to stdin. 10 sed -e '1,/^$/d' -e '/^[ ]*$/d' 11 # --> Delete empty lines and all lines until 12 # --> first one beginning with white space. 13 else 14 # ==> If command line args present, then work on files named. 15 for i do 16 sed -e '1,/^$/d' -e '/^[ ]*$/d' $i 17 # --> Ditto, as above. 18 done 19 fi 20 21 # ==> Exercise: Add error checking and other options. 22 # ==> 23 # ==> Note that the small sed script repeats, except for the arg passed. 24 # ==> Does it make sense to embed it in a function? Why or why not?
Example A-13. ftpget: Downloading files via ftp
https://www.xnip.cn/wp-content/uploads/2022/11/Example-A-13.txt
+
Antek Sawicki contributed the following script, which makes veryclever use of the parameter substitution operators discussed inSection 9.3.
Example A-14. password: Generating random8-character passwords
1 #!/bin/bash
2 # May need to be invoked with #!/bin/bash2 on older machines.
3 #
4 # Random password generator for Bash 2.x by Antek Sawicki <tenox@tenox.tc>,
5 # who generously gave permission to the document author to use it here.
6 #
7 # ==> Comments added by document author ==>
8
9
10 MATRIX="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
11 # ==> Password will consist of alphanumeric characters.
12 LENGTH="8"
13 # ==> May change 'LENGTH' for longer password.
14
15
16 while [ "${n:=1}" -le "$LENGTH" ]
17 # ==> Recall that := is "default substitution" operator.
18 # ==> So, if 'n' has not been initialized, set it to 1.
19 do
20 PASS="$PASS${MATRIX:$(($RANDOM%${#MATRIX})):1}"
21 # ==> Very clever, but tricky.
22
23 # ==> Starting from the innermost nesting...
24 # ==> ${#MATRIX} returns length of array MATRIX.
25
26 # ==> $RANDOM%${#MATRIX} returns random number between 1
27 # ==> and [length of MATRIX] - 1.
28
29 # ==> ${MATRIX:$(($RANDOM%${#MATRIX})):1}
30 # ==> returns expansion of MATRIX at random position, by length 1.
31 # ==> See {var:pos:len} parameter substitution in Chapter 9.
32 # ==> and the associated examples.
33
34 # ==> PASS=... simply pastes this result onto previous PASS (concatenation).
35
36 # ==> To visualize this more clearly, uncomment the following line
37 # echo "$PASS"
38 # ==> to see PASS being built up,
39 # ==> one character at a time, each iteration of the loop.
40
41 let n+=1
42 # ==> Increment 'n' for next pass.
43 done
44
45 echo "$PASS" # ==> Or, redirect to a file, as desired.
46
47 exit 0+
James R. Van Zandt contributed this script,which uses named pipes and, in his words, "really exercisesquoting and escaping".
Example A-15. fifo: Making daily backups, using named pipes
1 #!/bin/bash
2 # ==> Script by James R. Van Zandt, and used here with his permission.
3
4 # ==> Comments added by author of this document.
5
6
7 HERE=`uname -n` # ==> hostname
8 THERE=bilbo
9 echo "starting remote backup to $THERE at `date +%r`"
10 # ==> `date +%r` returns time in 12-hour format, i.e. "08:08:34 PM".
11
12 # make sure /pipe really is a pipe and not a plain file
13 rm -rf /pipe
14 mkfifo /pipe # ==> Create a "named pipe", named "/pipe".
15
16 # ==> 'su xyz' runs commands as user "xyz".
17 # ==> 'ssh' invokes secure shell (remote login client).
18 su xyz -c "ssh $THERE \"cat >/home/xyz/backup/${HERE}-daily.tar.gz\" < /pipe"&
19 cd /
20 tar -czf - bin boot dev etc home info lib man root sbin share usr var >/pipe
21 # ==> Uses named pipe, /pipe, to communicate between processes:
22 # ==> 'tar/gzip' writes to /pipe and 'ssh' reads from /pipe.
23
24 # ==> The end result is this backs up the main directories, from / on down.
25
26 # ==> What are the advantages of a "named pipe" in this situation,
27 # ==>+ as opposed to an "anonymous pipe", with |?
28 # ==> Will an anonymous pipe even work here?
29
30
31 exit 0+
St閜hane Chazelas contributed the following script todemonstrate that generating prime numbers does not requirearrays.
Example A-16. Generating prime numbers using the modulo operator
1 #!/bin/bash
2 # primes.sh: Generate prime numbers, without using arrays.
3 # Script contributed by Stephane Chazelas.
4
5 # This does *not* use the classic "Sieve of Eratosthenes" algorithm,
6 #+ but instead uses the more intuitive method of testing each candidate number
7 #+ for factors (divisors), using the "%" modulo operator.
8
9
10 LIMIT=1000 # Primes 2 - 1000
11
12 Primes()
13 {
14 (( n = $1 + 1 )) # Bump to next integer.
15 shift # Next parameter in list.
16 # echo "_n=$n i=$i_"
17
18 if (( n == LIMIT ))
19 then echo $*
20 return
21 fi
22
23 for i; do # "i" gets set to "@", previous values of $n.
24 # echo "-n=$n i=$i-"
25 (( i * i > n )) && break # Optimization.
26 (( n % i )) && continue # Sift out non-primes using modulo operator.
27 Primes $n $@ # Recursion inside loop.
28 return
29 done
30
31 Primes $n $@ $n # Recursion outside loop.
32 # Successively accumulate positional parameters.
33 # "$@" is the accumulating list of primes.
34 }
35
36 Primes 1
37
38 exit 0
39
40 # Uncomment lines 16 and 24 to help figure out what is going on.
41
42 # Compare the speed of this algorithm for generating primes
43 #+ with the Sieve of Eratosthenes (ex68.sh).
44
45 # Exercise: Rewrite this script without recursion, for faster execution.+
This is Rick Boivie's revision of Jordi Sanfeliu'streescript.
Example A-17. tree: Displaying a directory tree
1 #!/bin/bash
2 # tree.sh
3
4 # Written by Rick Boivie.
5 # Used with permission.
6 # This is a revised and simplified version of a script
7 #+ by Jordi Sanfeliu (and patched by Ian Kjos).
8 # This script replaces the earlier version used in
9 #+ previous releases of the Advanced Bash Scripting Guide.
10
11 # ==> Comments added by the author of this document.
12
13
14 search () {
15 for dir in `echo *`
16 # ==> `echo *` lists all the files in current working directory,
17 #+ ==> without line breaks.
18 # ==> Similar effect to for dir in *
19 # ==> but "dir in `echo *`" will not handle filenames with blanks.
20 do
21 if [ -d "$dir" ] ; then # ==> If it is a directory (-d)...
22 zz=0 # ==> Temp variable, keeping track of directory level.
23 while [ $zz != $1 ] # Keep track of inner nested loop.
24 do
25 echo -n "| " # ==> Display vertical connector symbol,
26 # ==> with 2 spaces & no line feed in order to indent.
27 zz=`expr $zz + 1` # ==> Increment zz.
28 done
29
30 if [ -L "$dir" ] ; then # ==> If directory is a symbolic link...
31 echo "+---$dir" `ls -l $dir | sed 's/^.*'$dir' //'`
32 # ==> Display horiz. connector and list directory name, but...
33 # ==> delete date/time part of long listing.
34 else
35 echo "+---$dir" # ==> Display horizontal connector symbol...
36 # ==> and print directory name.
37 numdirs=`expr $numdirs + 1` # ==> Increment directory count.
38 if cd "$dir" ; then # ==> If can move to subdirectory...
39 search `expr $1 + 1` # with recursion ;-)
40 # ==> Function calls itself.
41 cd ..
42 fi
43 fi
44 fi
45 done
46 }
47
48 if [ $# != 0 ] ; then
49 cd $1 # move to indicated directory.
50 #else # stay in current directory
51 fi
52
53 echo "Initial directory = `pwd`"
54 numdirs=0
55
56 search 0
57 echo "Total directories = $numdirs"
58
59 exit 0Noah Friedman gave permission to use his stringfunctionscript, which essentially reproduces some of theC-library string manipulation functions.
Example A-18. string functions: C-like string functions
https://www.xnip.cn/wp-content/uploads/2022/11/Example-A-18.txt
Michael Zick's complex array example uses the md5sumcheck sum command to encode directoryinformation.
Example A-19. Directory information
https://www.xnip.cn/wp-content/uploads/2022/11/Example-A-19.txt
Sthane Chazelas demonstrates object-oriented programming in aBash script.
Example A-20. Object-oriented database
1 #!/bin/bash
2 # obj-oriented.sh: Object-oriented programming in a shell script.
3 # Script by Stephane Chazelas.
4
5 # Important Note:
6 # --------- ----
7 # If running this script under version 3 or later of Bash,
8 #+ replace all periods in function names with a "legal" character,
9 #+ for example, an underscore.
10
11
12 person.new() # Looks almost like a class declaration in C++.
13 {
14 local obj_name=$1 name=$2 firstname=$3 birthdate=$4
15
16 eval "$obj_name.set_name() {
17 eval \"$obj_name.get_name() {
18 echo \$1
19 }\"
20 }"
21
22 eval "$obj_name.set_firstname() {
23 eval \"$obj_name.get_firstname() {
24 echo \$1
25 }\"
26 }"
27
28 eval "$obj_name.set_birthdate() {
29 eval \"$obj_name.get_birthdate() {
30 echo \$1
31 }\"
32 eval \"$obj_name.show_birthdate() {
33 echo \$(date -d \"1/1/1970 0:0:\$1 GMT\")
34 }\"
35 eval \"$obj_name.get_age() {
36 echo \$(( (\$(date +%s) - \$1) / 3600 / 24 / 365 ))
37 }\"
38 }"
39
40 $obj_name.set_name $name
41 $obj_name.set_firstname $firstname
42 $obj_name.set_birthdate $birthdate
43 }
44
45 echo
46
47 person.new self Bozeman Bozo 101272413
48 # Create an instance of "person.new" (actually passing args to the function).
49
50 self.get_firstname # Bozo
51 self.get_name # Bozeman
52 self.get_age # 28
53 self.get_birthdate # 101272413
54 self.show_birthdate # Sat Mar 17 20:13:33 MST 1973
55
56 echo
57
58 # typeset -f
59 #+ to see the created functions (careful, it scrolls off the page).
60
61 exit 0Mariusz Gniazdowski contributes a hashlibrary for use in scripts.
Example A-21. Library of hash functions
1 # Hash:
2 # Hash function library
3 # Author: Mariusz Gniazdowski <mgniazd-at-gmail.com>
4 # Date: 2005-04-07
5
6 # Functions making emulating hashes in Bash a little less painful.
7
8
9 # Limitations:
10 # * Only global variables are supported.
11 # * Each hash instance generates one global variable per value.
12 # * Variable names collisions are possible
13 #+ if you define variable like __hash__hashname_key
14 # * Keys must use chars that can be part of a Bash variable name
15 #+ (no dashes, periods, etc.).
16 # * The hash is created as a variable:
17 # ... hashname_keyname
18 # So if somone will create hashes like:
19 # myhash_ + mykey = myhash__mykey
20 # myhash + _mykey = myhash__mykey
21 # Then there will be a collision.
22 # (This should not pose a major problem.)
23
24
25 Hash_config_varname_prefix=__hash__
26
27
28 # Emulates: hash[key]=value
29 #
30 # Params:
31 # 1 - hash
32 # 2 - key
33 # 3 - value
34 function hash_set {
35 eval "${Hash_config_varname_prefix}${1}_${2}=\"${3}\""
36 }
37
38
39 # Emulates: value=hash[key]
40 #
41 # Params:
42 # 1 - hash
43 # 2 - key
44 # 3 - value (name of global variable to set)
45 function hash_get_into {
46 eval "$3=\"\$${Hash_config_varname_prefix}${1}_${2}\""
47 }
48
49
50 # Emulates: echo hash[key]
51 #
52 # Params:
53 # 1 - hash
54 # 2 - key
55 # 3 - echo params (like -n, for example)
56 function hash_echo {
57 eval "echo $3 \"\$${Hash_config_varname_prefix}${1}_${2}\""
58 }
59
60
61 # Emulates: hash1[key1]=hash2[key2]
62 #
63 # Params:
64 # 1 - hash1
65 # 2 - key1
66 # 3 - hash2
67 # 4 - key2
68 function hash_copy {
69 eval "${Hash_config_varname_prefix}${1}_${2}=\"\$${Hash_config_varname_prefix}${3}_${4}\""
70 }
71
72
73 # Emulates: hash[keyN-1]=hash[key2]=...hash[key1]
74 #
75 # Copies first key to rest of keys.
76 #
77 # Params:
78 # 1 - hash1
79 # 2 - key1
80 # 3 - key2
81 # . . .
82 # N - keyN
83 function hash_dup {
84 local hashName="$1" keyName="$2"
85 shift 2
86 until [ ${#} -le 0 ]; do
87 eval "${Hash_config_varname_prefix}${hashName}_${1}=\"\$${Hash_config_varname_prefix}${hashName}_${keyName}\""
88 shift;
89 done;
90 }
91
92
93 # Emulates: unset hash[key]
94 #
95 # Params:
96 # 1 - hash
97 # 2 - key
98 function hash_unset {
99 eval "unset ${Hash_config_varname_prefix}${1}_${2}"
100 }
101
102
103 # Emulates something similar to: ref=&hash[key]
104 #
105 # The reference is name of the variable in which value is held.
106 #
107 # Params:
108 # 1 - hash
109 # 2 - key
110 # 3 - ref - Name of global variable to set.
111 function hash_get_ref_into {
112 eval "$3=\"${Hash_config_varname_prefix}${1}_${2}\""
113 }
114
115
116 # Emulates something similar to: echo &hash[key]
117 #
118 # That reference is name of variable in which value is held.
119 #
120 # Params:
121 # 1 - hash
122 # 2 - key
123 # 3 - echo params (like -n for example)
124 function hash_echo_ref {
125 eval "echo $3 \"${Hash_config_varname_prefix}${1}_${2}\""
126 }
127
128
129
130 # Emulates something similar to: $$hash[key](param1, param2, ...)
131 #
132 # Params:
133 # 1 - hash
134 # 2 - key
135 # 3,4, ... - Function parameters
136 function hash_call {
137 local hash key
138 hash=$1
139 key=$2
140 shift 2
141 eval "eval \"\$${Hash_config_varname_prefix}${hash}_${key} \\\"\\\$@\\\"\""
142 }
143
144
145 # Emulates something similar to: isset(hash[key]) or hash[key]==NULL
146 #
147 # Params:
148 # 1 - hash
149 # 2 - key
150 # Returns:
151 # 0 - there is such key
152 # 1 - there is no such key
153 function hash_is_set {
154 eval "if [[ \"\${${Hash_config_varname_prefix}${1}_${2}-a}\" = \"a\" &&
155 \"\${${Hash_config_varname_prefix}${1}_${2}-b}\" = \"b\" ]]; then return 1; else return 0; fi"
156 }
157
158
159 # Emulates something similar to:
160 # foreach($hash as $key => $value) { fun($key,$value); }
161 #
162 # It is possible to write different variations of this function.
163 # Here we use a function call to make it as "generic" as possible.
164 #
165 # Params:
166 # 1 - hash
167 # 2 - function name
168 function hash_foreach {
169 local keyname oldIFS="$IFS"
170 IFS=' '
171 for i in $(eval "echo \${!${Hash_config_varname_prefix}${1}_*}"); do
172 keyname=$(eval "echo \${i##${Hash_config_varname_prefix}${1}_}")
173 eval "$2 $keyname \"\$$i\""
174 done
175 IFS="$oldIFS"
176 }
177
178 # NOTE: In lines 103 and 116, ampersand changed.
179 # But, it doesn't matter, because these are comment lines anyhow.Here is an example script using the foregoing hash library.
Example A-22. Colorizing text using hash functions
1 #!/bin/bash
2 # hash-example.sh: Colorizing text.
3 # Author: Mariusz Gniazdowski <mgniazd-at-gmail.com>
4
5 . Hash.lib # Load the library of functions.
6
7 hash_set colors red "\033[0;31m"
8 hash_set colors blue "\033[0;34m"
9 hash_set colors light_blue "\033[1;34m"
10 hash_set colors light_red "\033[1;31m"
11 hash_set colors cyan "\033[0;36m"
12 hash_set colors light_green "\033[1;32m"
13 hash_set colors light_gray "\033[0;37m"
14 hash_set colors green "\033[0;32m"
15 hash_set colors yellow "\033[1;33m"
16 hash_set colors light_purple "\033[1;35m"
17 hash_set colors purple "\033[0;35m"
18 hash_set colors reset_color "\033[0;00m"
19
20
21 # $1 - keyname
22 # $2 - value
23 try_colors() {
24 echo -en "$2"
25 echo "This line is $1."
26 }
27 hash_foreach colors try_colors
28 hash_echo colors reset_color -en
29
30 echo -e '\nLet us overwrite some colors with yellow.\n'
31 # It's hard to read yellow text on some terminals.
32 hash_dup colors yellow red light_green blue green light_gray cyan
33 hash_foreach colors try_colors
34 hash_echo colors reset_color -en
35
36 echo -e '\nLet us delete them and try colors once more . . .\n'
37
38 for i in red light_green blue green light_gray cyan; do
39 hash_unset colors $i
40 done
41 hash_foreach colors try_colors
42 hash_echo colors reset_color -en
43
44 hash_set other txt "Other examples . . ."
45 hash_echo other txt
46 hash_get_into other txt text
47 echo $text
48
49 hash_set other my_fun try_colors
50 hash_call other my_fun purple "`hash_echo colors purple`"
51 hash_echo colors reset_color -en
52
53 echo; echo "Back to normal?"; echo
54
55 exit $?
56
57 # On some terminals, the "light" colors print in bold,
58 # and end up looking darker than the normal ones.
59 # Why is this?
60 Now for a script that installs and mountsthose cute USB keychain solid-state "hard drives."
Example A-23. Mounting USB keychain storage devices
1 #!/bin/bash
2 # ==> usb.sh
3 # ==> Script for mounting and installing pen/keychain USB storage devices.
4 # ==> Runs as root at system startup (see below).
5 # ==>
6 # ==> Newer Linux distros (2004 or later) autodetect
7 # ==> and install USB pen drives, and therefore don't need this script.
8 # ==> But, it's still instructive.
9
10 # This code is free software covered by GNU GPL license version 2 or above.
11 # Please refer to http://www.gnu.org/ for the full license text.
12 #
13 # Some code lifted from usb-mount by Michael Hamilton's usb-mount (LGPL)
14 #+ see http://users.actrix.co.nz/michael/usbmount.html
15 #
16 # INSTALL
17 # -------
18 # Put this in /etc/hotplug/usb/diskonkey.
19 # Then look in /etc/hotplug/usb.distmap, and copy all usb-storage entries
20 #+ into /etc/hotplug/usb.usermap, substituting "usb-storage" for "diskonkey".
21 # Otherwise this code is only run during the kernel module invocation/removal
22 #+ (at least in my tests), which defeats the purpose.
23 #
24 # TODO
25 # ----
26 # Handle more than one diskonkey device at one time (e.g. /dev/diskonkey1
27 #+ and /mnt/diskonkey1), etc. The biggest problem here is the handling in
28 #+ devlabel, which I haven't yet tried.
29 #
30 # AUTHOR and SUPPORT
31 # ------------------
32 # Konstantin Riabitsev, <icon linux duke edu>.
33 # Send any problem reports to my email address at the moment.
34 #
35 # ==> Comments added by ABS Guide author.
36
37
38
39 SYMLINKDEV=/dev/diskonkey
40 MOUNTPOINT=/mnt/diskonkey
41 DEVLABEL=/sbin/devlabel
42 DEVLABELCONFIG=/etc/sysconfig/devlabel
43 IAM=$0
44
45 ##
46 # Functions lifted near-verbatim from usb-mount code.
47 #
48 function allAttachedScsiUsb {
49 find /proc/scsi/ -path '/proc/scsi/usb-storage*' -type f | xargs grep -l 'Attached: Yes'
50 }
51 function scsiDevFromScsiUsb {
52 echo $1 | awk -F"[-/]" '{ n=$(NF-1); print "/dev/sd" substr("abcdefghijklmnopqrstuvwxyz", n+1,
53 1) }'
54 }
55
56 if [ "${ACTION}" = "add" ] && [ -f "${DEVICE}" ]; then
57 ##
58 # lifted from usbcam code.
59 #
60 if [ -f /var/run/console.lock ]; then
61 CONSOLEOWNER=`cat /var/run/console.lock`
62 elif [ -f /var/lock/console.lock ]; then
63 CONSOLEOWNER=`cat /var/lock/console.lock`
64 else
65 CONSOLEOWNER=
66 fi
67 for procEntry in $(allAttachedScsiUsb); do
68 scsiDev=$(scsiDevFromScsiUsb $procEntry)
69 # Some bug with usb-storage?
70 # Partitions are not in /proc/partitions until they are accessed
71 #+ somehow.
72 /sbin/fdisk -l $scsiDev >/dev/null
73 ##
74 # Most devices have partitioning info, so the data would be on
75 #+ /dev/sd?1. However, some stupider ones don't have any partitioning
76 #+ and use the entire device for data storage. This tries to
77 #+ guess semi-intelligently if we have a /dev/sd?1 and if not, then
78 #+ it uses the entire device and hopes for the better.
79 #
80 if grep -q `basename $scsiDev`1 /proc/partitions; then
81 part="$scsiDev""1"
82 else
83 part=$scsiDev
84 fi
85 ##
86 # Change ownership of the partition to the console user so they can
87 #+ mount it.
88 #
89 if [ ! -z "$CONSOLEOWNER" ]; then
90 chown $CONSOLEOWNER:disk $part
91 fi
92 ##
93 # This checks if we already have this UUID defined with devlabel.
94 # If not, it then adds the device to the list.
95 #
96 prodid=`$DEVLABEL printid -d $part`
97 if ! grep -q $prodid $DEVLABELCONFIG; then
98 # cross our fingers and hope it works
99 $DEVLABEL add -d $part -s $SYMLINKDEV 2>/dev/null
100 fi
101 ##
102 # Check if the mount point exists and create if it doesn't.
103 #
104 if [ ! -e $MOUNTPOINT ]; then
105 mkdir -p $MOUNTPOINT
106 fi
107 ##
108 # Take care of /etc/fstab so mounting is easy.
109 #
110 if ! grep -q "^$SYMLINKDEV" /etc/fstab; then
111 # Add an fstab entry
112 echo -e \
113 "$SYMLINKDEV\t\t$MOUNTPOINT\t\tauto\tnoauto,owner,kudzu 0 0" \
114 >> /etc/fstab
115 fi
116 done
117 if [ ! -z "$REMOVER" ]; then
118 ##
119 # Make sure this script is triggered on device removal.
120 #
121 mkdir -p `dirname $REMOVER`
122 ln -s $IAM $REMOVER
123 fi
124 elif [ "${ACTION}" = "remove" ]; then
125 ##
126 # If the device is mounted, unmount it cleanly.
127 #
128 if grep -q "$MOUNTPOINT" /etc/mtab; then
129 # unmount cleanly
130 umount -l $MOUNTPOINT
131 fi
132 ##
133 # Remove it from /etc/fstab if it's there.
134 #
135 if grep -q "^$SYMLINKDEV" /etc/fstab; then
136 grep -v "^$SYMLINKDEV" /etc/fstab > /etc/.fstab.new
137 mv -f /etc/.fstab.new /etc/fstab
138 fi
139 fi
140
141 exit 0Here is something to warm the hearts of webmasters and mistresseseverywhere: a script that saves weblogs.
Example A-24. Preserving weblogs
1 #!/bin/bash 2 # archiveweblogs.sh v1.0 3 4 # Troy Engel <tengel@fluid.com> 5 # Slightly modified by document author. 6 # Used with permission. 7 # 8 # This script will preserve the normally rotated and 9 #+ thrown away weblogs from a default RedHat/Apache installation. 10 # It will save the files with a date/time stamp in the filename, 11 #+ bzipped, to a given directory. 12 # 13 # Run this from crontab nightly at an off hour, 14 #+ as bzip2 can suck up some serious CPU on huge logs: 15 # 0 2 * * * /opt/sbin/archiveweblogs.sh 16 17 18 PROBLEM=66 19 20 # Set this to your backup dir. 21 BKP_DIR=/opt/backups/weblogs 22 23 # Default Apache/RedHat stuff 24 LOG_DAYS="4 3 2 1" 25 LOG_DIR=/var/log/httpd 26 LOG_FILES="access_log error_log" 27 28 # Default RedHat program locations 29 LS=/bin/ls 30 MV=/bin/mv 31 ID=/usr/bin/id 32 CUT=/bin/cut 33 COL=/usr/bin/column 34 BZ2=/usr/bin/bzip2 35 36 # Are we root? 37 USER=`$ID -u` 38 if [ "X$USER" != "X0" ]; then 39 echo "PANIC: Only root can run this script!" 40 exit $PROBLEM 41 fi 42 43 # Backup dir exists/writable? 44 if [ ! -x $BKP_DIR ]; then 45 echo "PANIC: $BKP_DIR doesn't exist or isn't writable!" 46 exit $PROBLEM 47 fi 48 49 # Move, rename and bzip2 the logs 50 for logday in $LOG_DAYS; do 51 for logfile in $LOG_FILES; do 52 MYFILE="$LOG_DIR/$logfile.$logday" 53 if [ -w $MYFILE ]; then 54 DTS=`$LS -lgo --time-style=+%Y%m%d $MYFILE | $COL -t | $CUT -d ' ' -f7` 55 $MV $MYFILE $BKP_DIR/$logfile.$DTS 56 $BZ2 $BKP_DIR/$logfile.$DTS 57 else 58 # Only spew an error if the file exits (ergo non-writable). 59 if [ -f $MYFILE ]; then 60 echo "ERROR: $MYFILE not writable. Skipping." 61 fi 62 fi 63 done 64 done 65 66 exit 0
How do you keep the shell from expanding and reinterpretingstrings?
Example A-25. Protecting literal strings
1 #! /bin/bash
2 # protect_literal.sh
3
4 # set -vx
5
6 :<<-'_Protect_Literal_String_Doc'
7
8 Copyright (c) Michael S. Zick, 2003; All Rights Reserved
9 License: Unrestricted reuse in any form, for any purpose.
10 Warranty: None
11 Revision: $ID$
12
13 Documentation redirected to the Bash no-operation.
14 Bash will '/dev/null' this block when the script is first read.
15 (Uncomment the above set command to see this action.)
16
17 Remove the first (Sha-Bang) line when sourcing this as a library
18 procedure. Also comment out the example use code in the two
19 places where shown.
20
21
22 Usage:
23 _protect_literal_str 'Whatever string meets your ${fancy}'
24 Just echos the argument to standard out, hard quotes
25 restored.
26
27 $(_protect_literal_str 'Whatever string meets your ${fancy}')
28 as the right-hand-side of an assignment statement.
29
30 Does:
31 As the right-hand-side of an assignment, preserves the
32 hard quotes protecting the contents of the literal during
33 assignment.
34
35 Notes:
36 The strange names (_*) are used to avoid trampling on
37 the user's chosen names when this is sourced as a
38 library.
39
40 _Protect_Literal_String_Doc
41
42 # The 'for illustration' function form
43
44 _protect_literal_str() {
45
46 # Pick an un-used, non-printing character as local IFS.
47 # Not required, but shows that we are ignoring it.
48 local IFS=$'\x1B' # \ESC character
49
50 # Enclose the All-Elements-Of in hard quotes during assignment.
51 local tmp=$'\x27'$@$'\x27'
52 # local tmp=$'\''$@$'\'' # Even uglier.
53
54 local len=${#tmp} # Info only.
55 echo $tmp is $len long. # Output AND information.
56 }
57
58 # This is the short-named version.
59 _pls() {
60 local IFS=$'x1B' # \ESC character (not required)
61 echo $'\x27'$@$'\x27' # Hard quoted parameter glob
62 }
63
64 # :<<-'_Protect_Literal_String_Test'
65 # # # Remove the above "# " to disable this code. # # #
66
67 # See how that looks when printed.
68 echo
69 echo "- - Test One - -"
70 _protect_literal_str 'Hello $user'
71 _protect_literal_str 'Hello "${username}"'
72 echo
73
74 # Which yields:
75 # - - Test One - -
76 # 'Hello $user' is 13 long.
77 # 'Hello "${username}"' is 21 long.
78
79 # Looks as expected, but why all of the trouble?
80 # The difference is hidden inside the Bash internal order
81 #+ of operations.
82 # Which shows when you use it on the RHS of an assignment.
83
84 # Declare an array for test values.
85 declare -a arrayZ
86
87 # Assign elements with various types of quotes and escapes.
88 arrayZ=( zero "$(_pls 'Hello ${Me}')" 'Hello ${You}' "\'Pass: ${pw}\'" )
89
90 # Now list that array and see what is there.
91 echo "- - Test Two - -"
92 for (( i=0 ; i<${#arrayZ[*]} ; i++ ))
93 do
94 echo Element $i: ${arrayZ[$i]} is: ${#arrayZ[$i]} long.
95 done
96 echo
97
98 # Which yields:
99 # - - Test Two - -
100 # Element 0: zero is: 4 long. # Our marker element
101 # Element 1: 'Hello ${Me}' is: 13 long. # Our "$(_pls '...' )"
102 # Element 2: Hello ${You} is: 12 long. # Quotes are missing
103 # Element 3: \'Pass: \' is: 10 long. # ${pw} expanded to nothing
104
105 # Now make an assignment with that result.
106 declare -a array2=( ${arrayZ[@]} )
107
108 # And print what happened.
109 echo "- - Test Three - -"
110 for (( i=0 ; i<${#array2[*]} ; i++ ))
111 do
112 echo Element $i: ${array2[$i]} is: ${#array2[$i]} long.
113 done
114 echo
115
116 # Which yields:
117 # - - Test Three - -
118 # Element 0: zero is: 4 long. # Our marker element.
119 # Element 1: Hello ${Me} is: 11 long. # Intended result.
120 # Element 2: Hello is: 5 long. # ${You} expanded to nothing.
121 # Element 3: 'Pass: is: 6 long. # Split on the whitespace.
122 # Element 4: ' is: 1 long. # The end quote is here now.
123
124 # Our Element 1 has had its leading and trailing hard quotes stripped.
125 # Although not shown, leading and trailing whitespace is also stripped.
126 # Now that the string contents are set, Bash will always, internally,
127 #+ hard quote the contents as required during its operations.
128
129 # Why?
130 # Considering our "$(_pls 'Hello ${Me}')" construction:
131 # " ... " -> Expansion required, strip the quotes.
132 # $( ... ) -> Replace with the result of..., strip this.
133 # _pls ' ... ' -> called with literal arguments, strip the quotes.
134 # The result returned includes hard quotes; BUT the above processing
135 #+ has already been done, so they become part of the value assigned.
136 #
137 # Similarly, during further usage of the string variable, the ${Me}
138 #+ is part of the contents (result) and survives any operations
139 # (Until explicitly told to evaluate the string).
140
141 # Hint: See what happens when the hard quotes ($'\x27') are replaced
142 #+ with soft quotes ($'\x22') in the above procedures.
143 # Interesting also is to remove the addition of any quoting.
144
145 # _Protect_Literal_String_Test
146 # # # Remove the above "# " to disable this code. # # #
147
148 exit 0What if you wantthe shell to expandand reinterpret strings?
Example A-26. Unprotecting literal strings
1 #! /bin/bash
2 # unprotect_literal.sh
3
4 # set -vx
5
6 :<<-'_UnProtect_Literal_String_Doc'
7
8 Copyright (c) Michael S. Zick, 2003; All Rights Reserved
9 License: Unrestricted reuse in any form, for any purpose.
10 Warranty: None
11 Revision: $ID$
12
13 Documentation redirected to the Bash no-operation. Bash will
14 '/dev/null' this block when the script is first read.
15 (Uncomment the above set command to see this action.)
16
17 Remove the first (Sha-Bang) line when sourcing this as a library
18 procedure. Also comment out the example use code in the two
19 places where shown.
20
21
22 Usage:
23 Complement of the "$(_pls 'Literal String')" function.
24 (See the protect_literal.sh example.)
25
26 StringVar=$(_upls ProtectedSringVariable)
27
28 Does:
29 When used on the right-hand-side of an assignment statement;
30 makes the substitions embedded in the protected string.
31
32 Notes:
33 The strange names (_*) are used to avoid trampling on
34 the user's chosen names when this is sourced as a
35 library.
36
37
38 _UnProtect_Literal_String_Doc
39
40 _upls() {
41 local IFS=$'x1B' # \ESC character (not required)
42 eval echo $@ # Substitution on the glob.
43 }
44
45 # :<<-'_UnProtect_Literal_String_Test'
46 # # # Remove the above "# " to disable this code. # # #
47
48
49 _pls() {
50 local IFS=$'x1B' # \ESC character (not required)
51 echo $'\x27'$@$'\x27' # Hard quoted parameter glob
52 }
53
54 # Declare an array for test values.
55 declare -a arrayZ
56
57 # Assign elements with various types of quotes and escapes.
58 arrayZ=( zero "$(_pls 'Hello ${Me}')" 'Hello ${You}' "\'Pass: ${pw}\'" )
59
60 # Now make an assignment with that result.
61 declare -a array2=( ${arrayZ[@]} )
62
63 # Which yielded:
64 # - - Test Three - -
65 # Element 0: zero is: 4 long # Our marker element.
66 # Element 1: Hello ${Me} is: 11 long # Intended result.
67 # Element 2: Hello is: 5 long # ${You} expanded to nothing.
68 # Element 3: 'Pass: is: 6 long # Split on the whitespace.
69 # Element 4: ' is: 1 long # The end quote is here now.
70
71 # set -vx
72
73 # Initialize 'Me' to something for the embedded ${Me} substitution.
74 # This needs to be done ONLY just prior to evaluating the
75 #+ protected string.
76 # (This is why it was protected to begin with.)
77
78 Me="to the array guy."
79
80 # Set a string variable destination to the result.
81 newVar=$(_upls ${array2[1]})
82
83 # Show what the contents are.
84 echo $newVar
85
86 # Do we really need a function to do this?
87 newerVar=$(eval echo ${array2[1]})
88 echo $newerVar
89
90 # I guess not, but the _upls function gives us a place to hang
91 #+ the documentation on.
92 # This helps when we forget what a # construction like:
93 #+ $(eval echo ... ) means.
94
95 # What if Me isn't set when the protected string is evaluated?
96 unset Me
97 newestVar=$(_upls ${array2[1]})
98 echo $newestVar
99
100 # Just gone, no hints, no runs, no errors.
101
102 # Why in the world?
103 # Setting the contents of a string variable containing character
104 #+ sequences that have a meaning in Bash is a general problem in
105 #+ script programming.
106 #
107 # This problem is now solved in eight lines of code
108 #+ (and four pages of description).
109
110 # Where is all this going?
111 # Dynamic content Web pages as an array of Bash strings.
112 # Content set per request by a Bash 'eval' command
113 #+ on the stored page template.
114 # Not intended to replace PHP, just an interesting thing to do.
115 ###
116 # Don't have a webserver application?
117 # No problem, check the example directory of the Bash source;
118 #+ there is a Bash script for that also.
119
120 # _UnProtect_Literal_String_Test
121 # # # Remove the above "# " to disable this code. # # #
122
123 exit 0This powerful script helps hunt down spammers.
Example A-27. Spammer Identification
https://www.xnip.cn/wp-content/uploads/2022/11/Example-A-27.txt
Another anti-spam script.
Example A-28. Spammer Hunt
https://www.xnip.cn/wp-content/uploads/2022/11/Example-A-28.txt
"Little Monster's"front end to wget.
Example A-29. Making wgeteasier to use
https://www.xnip.cn/wp-content/uploads/2022/11/Example-A-29.txt
Example A-30. A "podcasting"script
1 #!/bin/bash 2 3 # bashpodder.sh: 4 # By Linc 10/1/2004 5 # Find the latest script at http://linc.homeunix.org:8080/scripts/bashpodder 6 # Last revision 12/14/2004 - Many Contributors! 7 # If you use this and have made improvements or have comments 8 # drop me an email at linc dot fessenden at gmail dot com 9 # I'd appreciate it! 10 11 # ==> ABS Guide extra comments. 12 13 # ==> Author of this script has kindly granted permission 14 # ==>+ for inclusion in ABS Guide. 15 16 17 # ==> ################################################################ 18 # 19 # ==> What is "podcasting"? 20 21 # ==> It's broadcasting "radio shows" over the Internet. 22 # ==> These shows can be played on iPods and other music file players. 23 24 # ==> This script makes it possible. 25 # ==> See documentation at the script author's site, above. 26 27 # ==> ################################################################ 28 29 30 # Make script crontab friendly: 31 cd $(dirname $0) 32 # ==> Change to directory where this script lives. 33 34 # datadir is the directory you want podcasts saved to: 35 datadir=$(date +%Y-%m-%d) 36 # ==> Will create a directory with the name: YYYY-MM-DD 37 38 # Check for and create datadir if necessary: 39 if test ! -d $datadir 40 then 41 mkdir $datadir 42 fi 43 44 # Delete any temp file: 45 rm -f temp.log 46 47 # Read the bp.conf file and wget any url not already in the podcast.log file: 48 while read podcast 49 do # ==> Main action follows. 50 file=$(wget -q $podcast -O - | tr '\r' '\n' | tr \' \" | sed -n 's/.*url="\([^"]*\)".*/\1/p') 51 for url in $file 52 do 53 echo $url >> temp.log 54 if ! grep "$url" podcast.log > /dev/null 55 then 56 wget -q -P $datadir "$url" 57 fi 58 done 59 done < bp.conf 60 61 # Move dynamically created log file to permanent log file: 62 cat podcast.log >> temp.log 63 sort temp.log | uniq > podcast.log 64 rm temp.log 65 # Create an m3u playlist: 66 ls $datadir | grep -v m3u > $datadir/podcast.m3u 67 68 69 exit 0
To end this section, a review of the basics . . . and more.
Example A-31. Basics Reviewed
https://www.xnip.cn/wp-content/uploads/2022/11/Example-A-31.txt
Example A-32. An expanded cdcommand
https://www.xnip.cn/wp-content/uploads/2022/11/Example-A-32.txt