33.2. Shell Wrappers

   1 #!/bin/bash
   2 
   3 # This is a simple script that removes blank lines from a file.
   4 # No argument checking.
   5 #
   6 # You might wish to add something like:
   7 #
   8 # E_NOARGS=65
   9 # if [ -z "$1" ]
  10 # then
  11 #  echo "Usage: `basename $0` target-file"
  12 #  exit $E_NOARGS
  13 # fi
  14 
  15 
  16 # Same as
  17 #    sed -e '/^$/d' filename
  18 # invoked from the command line.
  19 
  20 sed -e /^$/d "$1"
  21 #  The '-e' means an "editing" command follows (optional here).
  22 #  '^' is the beginning of line, '$' is the end.
  23 #  This match lines with nothing between the beginning and the end,
  24 #+ blank lines.
  25 #  The 'd' is the delete command.
  26 
  27 #  Quoting the command-line arg permits
  28 #+ whitespace and special characters in the filename.
  29 
  30 #  Note that this script doesn't actually change the target file.
  31 #  If you need to do that, redirect its output.
  32 
  33 exit 0

   1 #!/bin/bash
   2 
   3 #  "subst", a script that substitutes one pattern for
   4 #+ another in a file,
   5 #+ i.e., "subst Smith Jones letter.txt".
   6 
   7 ARGS=3         # Script requires 3 arguments.
   8 E_BADARGS=65   # Wrong number of arguments passed to script.
   9 
  10 if [ $# -ne "$ARGS" ]
  11 # Test number of arguments to script (always a good idea).
  12 then
  13   echo "Usage: `basename $0` old-pattern new-pattern filename"
  14   exit $E_BADARGS
  15 fi
  16 
  17 old_pattern=$1
  18 new_pattern=$2
  19 
  20 if [ -f "$3" ]
  21 then
  22     file_name=$3
  23 else
  24     echo "File \"$3\" does not exist."
  25     exit $E_BADARGS
  26 fi
  27 
  28 
  29 #  Here is where the heavy work gets done.
  30 
  31 # -----------------------------------------------
  32 sed -e "s/$old_pattern/$new_pattern/g" $file_name
  33 # -----------------------------------------------
  34 
  35 #  's' is, of course, the substitute command in sed,
  36 #+ and /pattern/ invokes address matching.
  37 #  The "g", or global flag causes substitution for *every*
  38 #+ occurence of $old_pattern on each line, not just the first.
  39 #  Read the literature on 'sed' for an in-depth explanation.
  40 
  41 exit 0    # Successful invocation of the script returns 0.

   1 #!/bin/bash
   2 #  Generic shell wrapper that performs an operation
   3 #+ and logs it.
   4 
   5 # Must set the following two variables.
   6 OPERATION=
   7 #         Can be a complex chain of commands,
   8 #+        for example an awk script or a pipe . . .
   9 LOGFILE=
  10 #         Command-line arguments, if any, for the operation.
  11 
  12 
  13 OPTIONS="$@"
  14 
  15 
  16 # Log it.
  17 echo "`date` + `whoami` + $OPERATION "$@"" >> $LOGFILE
  18 # Now, do it.
  19 exec $OPERATION "$@"
  20 
  21 # It's necessary to do the logging before the operation.
  22 # Why?

   1 #!/bin/bash
   2 # pr-ascii.sh: Prints a table of ASCII characters.
   3 
   4 START=33   # Range of printable ASCII characters (decimal).
   5 END=125
   6 
   7 echo " Decimal   Hex     Character"   # Header.
   8 echo " -------   ---     ---------"
   9 
  10 for ((i=START; i<=END; i++))
  11 do
  12   echo $i | awk '{printf("  %3d       %2x         %c\n", $1, $1, $1)}'
  13 # The Bash printf builtin will not work in this context:
  14 #     printf "%c" "$i"
  15 done
  16 
  17 exit 0
  18 
  19 
  20 #  Decimal   Hex     Character
  21 #  -------   ---     ---------
  22 #    33       21         !
  23 #    34       22         "
  24 #    35       23         #
  25 #    36       24         $
  26 #
  27 #    . . .
  28 #
  29 #   122       7a         z
  30 #   123       7b         {
  31 #   124       7c         |
  32 #   125       7d         }
  33 
  34 
  35 #  Redirect the output of this script to a file
  36 #+ or pipe it to "more":  sh pr-asc.sh | more

   1 #!/bin/bash
   2 
   3 # Adds up a specified column (of numbers) in the target file.
   4 
   5 ARGS=2
   6 E_WRONGARGS=65
   7 
   8 if [ $# -ne "$ARGS" ] # Check for proper no. of command line args.
   9 then
  10    echo "Usage: `basename $0` filename column-number"
  11    exit $E_WRONGARGS
  12 fi
  13 
  14 filename=$1
  15 column_number=$2
  16 
  17 #  Passing shell variables to the awk part of the script is a bit tricky.
  18 #  One method is to strong-quote the Bash-script variable
  19 #+ within the awk script.
  20 #     $'$BASH_SCRIPT_VAR'
  21 #      ^                ^
  22 #  This is done in the embedded awk script below.
  23 #  See the awk documentation for more details.
  24 
  25 # A multi-line awk script is invoked by:  awk ' ..... '
  26 
  27 
  28 # Begin awk script.
  29 # -----------------------------
  30 awk '
  31 
  32 { total += $'"${column_number}"'
  33 }
  34 END {
  35      print total
  36 }     
  37 
  38 ' "$filename"
  39 # -----------------------------
  40 # End awk script.
  41 
  42 
  43 #   It may not be safe to pass shell variables to an embedded awk script,
  44 #+  so Stephane Chazelas proposes the following alternative:
  45 #   ---------------------------------------
  46 #   awk -v column_number="$column_number" '
  47 #   { total += $column_number
  48 #   }
  49 #   END {
  50 #       print total
  51 #   }' "$filename"
  52 #   ---------------------------------------
  53 
  54 
  55 exit 0

   1 #!/bin/bash
   2 
   3 # Shell commands may precede the Perl script.
   4 echo "This precedes the embedded Perl script within \"$0\"."
   5 echo "==============================================================="
   6 
   7 perl -e 'print "This is an embedded Perl script.\n";'
   8 # Like sed, Perl also uses the "-e" option.
   9 
  10 echo "==============================================================="
  11 echo "However, the script may also contain shell and system commands."
  12 
  13 exit 0

   1 #!/bin/bash
   2 # bashandperl.sh
   3 
   4 echo "Greetings from the Bash part of the script."
   5 # More Bash commands may follow here.
   6 
   7 exit 0
   8 # End of Bash part of the script.
   9 
  10 # =======================================================
  11 
  12 #!/usr/bin/perl
  13 # This part of the script must be invoked with -x option.
  14 
  15 print "Greetings from the Perl part of the script.\n";
  16 # More Perl commands may follow here.
  17 
  18 # End of Perl part of the script.