36.2. Shell Wrappers

   1 #!/bin/bash
   2 
   3 # This simple script removes blank lines from a file.
   4 # No argument checking.
   5 #
   6 # You might wish to add something like:
   7 #
   8 # E_NOARGS=85
   9 # if [ -z "$1" ]
  10 # then
  11 #  echo "Usage: `basename $0` target-file"
  12 #  exit $E_NOARGS
  13 # fi
  14 
  15 
  16 
  17 sed -e /^$/d "$1"
  18 # Same as
  19 #    sed -e '/^$/d' filename
  20 # invoked from the command-line.
  21 
  22 #  The '-e' means an "editing" command follows (optional here).
  23 #  '^' indicates the beginning of line, '$' the end.
  24 #  This matches lines with nothing between the beginning and the end --
  25 #+ blank lines.
  26 #  The 'd' is the delete command.
  27 
  28 #  Quoting the command-line arg permits
  29 #+ whitespace and special characters in the filename.
  30 
  31 #  Note that this script doesn't actually change the target file.
  32 #  If you need to do that, redirect its output.
  33 
  34 exit

   1 #!/bin/bash
   2 
   3 #  subst.sh: a script that substitutes one pattern for
   4 #+ another in a file,
   5 #+ i.e., "sh subst.sh Smith Jones letter.txt".
   6 #                     Jones replaces Smith.
   7 
   8 ARGS=3         # Script requires 3 arguments.
   9 E_BADARGS=85   # Wrong number of arguments passed to script.
  10 
  11 if [ $# -ne "$ARGS" ]
  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 $E_BADARGS
  26 fi
  27 
  28 
  29 # -----------------------------------------------
  30 #  Here is where the heavy work gets done.
  31 sed -e "s/$old_pattern/$new_pattern/g" $file_name
  32 # -----------------------------------------------
  33 
  34 #  's' is, of course, the substitute command in sed,
  35 #+ and /pattern/ invokes address matching.
  36 #  The 'g,' or global flag causes substitution for EVERY
  37 #+ occurence of $old_pattern on each line, not just the first.
  38 #  Read the 'sed' docs for an in-depth explanation.
  39 
  40 exit $?  # Redirect the output of this script to write to a file.

   1 #!/bin/bash
   2 #  logging-wrapper.sh
   3 #  Generic shell wrapper that performs an operation
   4 #+ and logs it.
   5 
   6 DEFAULT_LOGFILE=logfile.txt
   7 
   8 # Set the following two variables.
   9 OPERATION=
  10 #         Can be a complex chain of commands,
  11 #+        for example an awk script or a pipe . . .
  12 
  13 LOGFILE=
  14 if [ -z "$LOGFILE" ]
  15 then     # If not set, default to ...
  16   LOGFILE="$DEFAULT_LOGFILE"
  17 fi
  18 
  19 #         Command-line arguments, if any, for the operation.
  20 OPTIONS="$@"
  21 
  22 
  23 # Log it.
  24 echo "`date` + `whoami` + $OPERATION "$@"" >> $LOGFILE
  25 # Now, do it.
  26 exec $OPERATION "$@"
  27 
  28 # It's necessary to do the logging before the operation.
  29 # 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=127    # Will not work for unprintable characters (> 127).
   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 # Floating-point (decimal) numbers okay, because awk can handle them.
   5 
   6 ARGS=2
   7 E_WRONGARGS=85
   8 
   9 if [ $# -ne "$ARGS" ] # Check for proper number of command-line args.
  10 then
  11    echo "Usage: `basename $0` filename column-number"
  12    exit $E_WRONGARGS
  13 fi
  14 
  15 filename=$1
  16 column_number=$2
  17 
  18 #  Passing shell variables to the awk part of the script is a bit tricky.
  19 #  One method is to strong-quote the Bash-script variable
  20 #+ within the awk script.
  21 #     $'$BASH_SCRIPT_VAR'
  22 #      ^                ^
  23 #  This is done in the embedded awk script below.
  24 #  See the awk documentation for more details.
  25 
  26 # A multi-line awk script is here invoked by
  27 #   awk '
  28 #   ...
  29 #   ...
  30 #   ...
  31 #   '
  32 
  33 
  34 # Begin awk script.
  35 # -----------------------------
  36 awk '
  37 
  38 { total += $'"${column_number}"'
  39 }
  40 END {
  41      print total
  42 }     
  43 
  44 ' "$filename"
  45 # -----------------------------
  46 # End awk script.
  47 
  48 
  49 #   It may not be safe to pass shell variables to an embedded awk script,
  50 #+  so Stephane Chazelas proposes the following alternative:
  51 #   ---------------------------------------
  52 #   awk -v column_number="$column_number" '
  53 #   { total += $column_number
  54 #   }
  55 #   END {
  56 #       print total
  57 #   }' "$filename"
  58 #   ---------------------------------------
  59 
  60 
  61 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 line prints from 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, $0."
   5 # More Bash commands may follow here.
   6 
   7 exit
   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
  14 #    perl -x bashandperl.sh
  15 
  16 print "Greetings from the Perl part of the script, $0.\n";
  17 #      Perl doesn't seem to like "echo" ...
  18 # More Perl commands may follow here.
  19 
  20 # End of Perl part of the script.

   1 #!/bin/bash
   2 # ex56py.sh
   3 
   4 # Shell commands may precede the Python script.
   5 echo "This precedes the embedded Python script within \"$0.\""
   6 echo "==============================================================="
   7 
   8 python -c 'print "This line prints from an embedded Python script.\n";'
   9 # Unlike sed and perl, Python uses the "-c" option.
  10 python -c 'k = raw_input( "Hit a key to exit to outer script. " )'
  11 
  12 echo "==============================================================="
  13 echo "However, the script may also contain shell and system commands."
  14 
  15 exit 0

   1 #!/bin/bash
   2 #   Courtesy of:
   3 #   http://elinux.org/RPi_Text_to_Speech_(Speech_Synthesis)
   4 
   5 #  You must be on-line for this script to work,
   6 #+ so you can access the Google translation server.
   7 #  Of course, mplayer must be present on your computer.
   8 
   9 speak()
  10   {
  11   local IFS=+
  12   # Invoke mplayer, then connect to Google translation server.
  13   /usr/bin/mplayer -ao alsa -really-quiet -noconsolecontrols \
  14  "http://translate.google.com/translate_tts?tl=en&q="$*""
  15   # Google translates, but can also speak.
  16   }
  17 
  18 LINES=4
  19 
  20 spk=$(tail -$LINES $0) # Tail end of same script!
  21 speak "$spk"
  22 exit
  23 # Browns. Nice talking to you.