Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
Example 10−28. Checking for alphabetic input
#!/bin/bash
# isalpha.sh: Using a "case" structure to filter a string.
SUCCESS=0
FAILURE=−1
isalpha () # Tests whether *first character* of input string is alphabetic.
{
if [ −z "$1" ]
# No argument passed?
then
return $FAILURE
fi
case "$1" in
[a−zA−Z]*) return $SUCCESS;; # Begins with a letter?
* ) return $FAILURE;;
esac
} # Compare this with "isalpha ()" function in C.
isalpha2 () # Tests whether *entire string* is alphabetic.
{
[ $# −eq 1 ] || return $FAILURE
}
case $1 in
*[!a−zA−Z]*|"") return $FAILURE;;
*) return $SUCCESS;;
esac
isdigit () # Tests whether *entire string* is numerical.
{ # In other words, tests for integer variable.
[ $# −eq 1 ] || return $FAILURE
}
case $1 in
*[!0−9]*|"") return $FAILURE;;
*) return $SUCCESS;;
esac
check_var () # Front−end to isalpha ().
{
if isalpha "$@"
then
echo "\"$*\" begins with an alpha character."
if isalpha2 "$@"
then # No point in testing if first char is non−alpha.
echo "\"$*\" contains only alpha characters."
else
echo "\"$*\" contains at least one non−alpha character."
fi
else
echo "\"$*\" begins with a non−alpha character."
# Also "non−alpha" if no argument passed.
fi
echo
Chapter 10. Loops and Branches 121