Bash/Parsing command line arguments using getopts - Revision history

Bandtank: moved Bash/commandLineArgs to Bash/Parsing command line arguments using getopts

2011-10-05T16:41:25Z

moved Bash/commandLineArgs to Bash/Parsing command line arguments using getopts

Bandtank at 02:02, 5 October 2011

2011-10-05T02:02:31Z

Bandtank at 01:56, 5 October 2011

2011-10-05T01:56:26Z

Griswolf: Add example of handling command line arguments

2011-04-21T00:59:17Z

Add example of handling command line arguments

New page

This is an example of looping over the command line parameters, handling flags and arguments. To do it right, I ended up showing several other things too. The critical bits are
* looping by checking the number of remaining args '''$#'''
* using '''case / esac''', case tags '''xxx)''', '''shift''' and ''';;'''
* using '''cat <<EOM''' ... '''EOM''' to provide a multi-line message

<syntaxhighlight lang="bash">
#!/bin/bash

globalVariableStrings='' # by default, bash variables are strings
declare -i globalVariableInt=0 # but if you know it's an int, declare it so
while [[ $# -gt 0 ]] ; do # $# is the count of command line args
case $1 in # $1 is the first (remaining) arg.
# case tags can be simple regular expressions. cat <<EOM cats everything up to a solo EOM on a line
-h|--h*)cat <<EOM
Usage: $(basename $0) [flags] [arguments]
-h/--help: Show this message and exit
-i value /--int=value: handle an integer flag. Last one wins
<argument> handle a non-flag argument. Each seen is appended
EOM
exit 0 ;; # exit 0 flags 'success'. ;; shows end of a case statement
-i) shift; # shift removes the first arg (-i here)
globalVariableInt=$1 # set the integer value
shift ;; # remove the integer value and drop from the case block
--int=*)
globalVariableInt=$(echo $1|cut -f2 -d=) # -f: Which field; -d: what delimiter
shift ;; # as always
*) globalVariableStrings="$globalVariableStrings $1" # append argument
shift ;; # as always
esac
done
echo "The integer is $globalVariableInt"
for s in $globalVariableStrings ; do
echo "You entered argument '$s'"
done
</syntaxhighlight>

@@ Line 34: / Line 34: @@
 #Process the arguments
-while getopts c:hi: opt
+while getopts c:hin: opt
 do
     case "$opt" in
        c) cell=$OPTARG;;
        h) usage;;
        n) name=$OPTARG;;
        \?) usage;;
@@ Line 50: / Line 51: @@
 <syntaxhighlight lang="bash">
 getopts_example.sh -c test1 -n test2
-getopts_example.sh -c test3
+getopts_example.sh -c test3 -i
 getopts_example.sh -h
 getopts_example.sh -a
@@ Line 58: / Line 59: @@
 Example 1 would assign "test1" to the $cell variable and "test2" to the $name variable.
-Example 2 would assign "test3" to the $cell variable and $name would not exist.
+Example 2 would assign "test3" to the $cell variable, $name would not exist, and "yes" would be assigned to $info.
 Example 3 would call the usage function.
 Example 4 would cause getopts to display an error to stderr and then exit after calling the usage function.

← Older revision	Revision as of 16:41, 5 October 2011
(No difference)

@@ Line 1: / Line 1: @@
-This is an example of looping over the command line parameters, handling flags and arguments. To do it right, I ended up showing several other things too. The critical bits are
+Handling command line arguments can be done many ways, but few will be as elegant and streamlined as the built-in shell command called getopts. Note: getopt is the older version and should not be used as it is far less robust.
-* looping by checking the number of remaining args '''$#'''
-* using '''case / esac''', case tags '''xxx)''', '''shift''' and ''';;'''
+Getopts shifts the data and sets an exit status of false when there is nothing left to do. Because of this behavior, getopts works well in a while loop as follows:
-* using '''cat <<EOM''' ... '''EOM''' to provide a multi-line message
 <syntaxhighlight lang="bash">
 #!/bin/bash
-globalVariableStrings=''  # by default, bash variables are strings
+#Set a default value for the $cell variable
-declare -i globalVariableInt=0 # but if you know it's an int, declare it so
+cell="test"
-while [[ $# -gt 0 ]] ; do # $# is the count of command line args
-  case $1 in              # $1 is the first (remaining) arg.
+#Check to see if at least one argument was specified
-  # case tags can be simple regular expressions. cat <<EOM cats everything up to a solo EOM on a line
+if [ $# -lt 1 ] ; then
-  -h|--h*)cat <<EOM
+   echo "You must specify at least 1 argument."
-Usage: $(basename $0) [flags] [arguments]
+   exit 1
- -h/--help: Show this message and exit
+fi
- -i value /--int=value: handle an integer flag. Last one wins
- <argument> handle a non-flag argument. Each seen is appended
+#Process the arguments
-EOM
+while getopts c:hi: opt
-  exit 0 ;;               # exit 0 flags 'success'. ;; shows end of a case statement
+do
-  -i) shift;              # shift removes the first arg (-i here)
+   case "$opt" in
-       globalVariableInt=$1  # set the integer value
+      c) cell=$OPTARG;;
-       shift ;;           # remove the integer value and drop from the case block
+      h) usage;;
-  --int=*)
+      n) name=$OPTARG;;
-       globalVariableInt=$(echo $1|cut -f2 -d=) # -f: Which field; -d: what delimiter
+      \?) usage;;
-       shift ;;           # as always
+   esac
-  *) globalVariableStrings="$globalVariableStrings $1" # append argument
-     shift ;;             # as always
-  esac
-done
-echo "The integer is $globalVariableInt"
-for s in $globalVariableStrings ; do
-  echo "You entered argument '$s'"
 done
 </syntaxhighlight>