2.2. Shell wrapper, self-executing script

   1 #!/bin/bash
   2 
   3 # This is a simple script that removes blank lines from a file.
   4 # No argument checking.
   5 
   6 # Same as
   7 #    sed -e '/^$/d' filename
   8 # invoked from the command line.
   9 
  10 sed -e /^$/d "$1"
  11 # The '-e' means an "editing" command follows (optional here).
  12 # '^' is beginning of line,
  13 # '$' is end,
  14 # and 'd' is delete.
  15 # Quoting the command-line arg permits special chars in the filename.
  16 
  17 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
   8 E_BADARGS=65   # Wrong number of arguments passed to script.
   9 
  10 if [ $# -ne "$ARGS" ]
  11 # Test number of arguments to script
  12 # (always a good idea).
  13 then
  14   echo "Usage: `basename $0` old-pattern new-pattern filename"
  15   exit $E_BADARGS
  16 fi
  17 
  18 old_pattern=$1
  19 new_pattern=$2
  20 
  21 if [ -f "$3" ]
  22 then
  23     file_name=$3
  24 else
  25     echo "File \"$3\" does not exist."
  26     exit $E_BADARGS
  27 fi
  28 
  29 # Here is where the heavy work gets done.
  30 sed -e "s/$old_pattern/$new_pattern/g" $file_name
  31 # 's' is, of course, the substitute command in sed,
  32 # and /pattern/ invokes address matching.
  33 # The "g", or global flag causes substitution for *every*
  34 # occurence of $old_pattern on each line, not just the first.
  35 # Read the literature on 'sed' for a more
  36 # in-depth explanation.
  37 
  38 exit 0
  39 # Successful invocation of the script returns 0.

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

   1 #!/bin/bash
   2 
   3 # Some shell commands may precede the Perl script.
   4 
   5 perl -e 'print "This is an embedded Perl script\n"'
   6 # Like sed and awk, Perl also uses the "-e" option.
   7 
   8 # Some shell commands may follow.
   9 
  10 exit 0