Advanced Bash−Scripting Guide

# The 'd' is the delete command.
# Quoting the command−line arg permits
#+ whitespace and special characters in the filename.
exit 0
Advanced Bash−Scripting Guide
Example 34−2. A slightly more complex shell wrapper
#!/bin/bash
# "subst", a script that substitutes one pattern for
# another in a file,
# i.e., "subst Smith Jones letter.txt".
ARGS=3
E_BADARGS=65
# Wrong number of arguments passed to script.
if [ $# −ne "$ARGS" ]
# Test number of arguments to script (always a good idea).
then
echo "Usage: `basename $0` old−pattern new−pattern filename"
exit $E_BADARGS
fi
old_pattern=$1
new_pattern=$2
if [ −f "$3" ]
then
file_name=$3
else
echo "File \"$3\" does not exist."
exit $E_BADARGS
fi
# Here is where the heavy work gets done.
sed −e "s/$old_pattern/$new_pattern/g" $file_name
# 's' is, of course, the substitute command in sed,
# and /pattern/ invokes address matching.
# The "g", or global flag causes substitution for *every*
# occurence of $old_pattern on each line, not just the first.
# Read the literature on 'sed' for a more in−depth explanation.
exit 0 # Successful invocation of the script returns 0.
Example 34−3. A shell wrapper around an awk script
#!/bin/bash
# Adds up a specified column (of numbers) in the target file.
ARGS=2
E_WRONGARGS=65
if [ $# −ne "$ARGS" ] # Check for proper no. of command line args.
then
echo "Usage: `basename $0` filename column−number"
Chapter 34. Miscellany 338