Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
then
# then
let "return_val = (( 0 − $return_val ))" # renormalize to positive.
fi
# "Absolute value" of $return_val.
# −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− #
if [ "$return_val" −eq "$E_NPARAM_ERR" ]
then
# Parameter error "flag" gets sign changed, too.
echo "Error: Too few parameters."
elif [ "$return_val" −eq "$EQUAL" ]
then
echo "The two numbers are equal."
else
echo "The larger of the two numbers is $return_val."
fi
exit 0
See also Example A−8.
Exercise: Using what we have just learned, extend the previous Roman numerals example to
accept arbitrarily large input.
Redirection
Redirecting the stdin of a function
A function is essentially a code block, which means its stdin can be redirected (as in Example 3−1).
Example 23−7. Real name from username
#!/bin/bash
# From username, gets "real name" from /etc/passwd.
ARGCOUNT=1 # Expect one arg.
E_WRONGARGS=65
file=/etc/passwd
pattern=$1
if [ $# −ne "$ARGCOUNT" ]
then
echo "Usage: `basename $0` USERNAME"
exit $E_WRONGARGS
fi
file_excerpt () # Scan file for pattern, the print relevant portion of line.
{
while read line # while does not necessarily need "[ condition]"
do
echo "$line" | grep $1 | awk −F":" '{ print $5 }' # Have awk use ":" delimiter.
done
}