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New page: BASH provides a number of flow control constructs. = if = Format: if ''pipeline'' then ''success-commands'' <nowiki>[</nowiki>elif ''pipeline2'' ''else-if-commands'' <nowi...
[[BASH]] provides a number of flow control constructs.
= if =
Format:
if ''pipeline''
then
''success-commands''
<nowiki>[</nowiki>elif ''pipeline2''
''else-if-commands''
<nowiki>]</nowiki>
<nowiki>[else</nowiki>
''alt-commands''
<nowiki>]</nowiki>
fi
Executes ''success-commands'' if ''pipeline'' returns an exit code of zero.
If ''success-commands'' returns a non-zero exit code and ''pipeline2'' returns an exit code of zero, executes ''else-if-commands''.
Otherwise, executes ''alt-commands''.
Examples:
if grep -q "jason" /etc/passwd
then
echo "the user 'jason' exists in the passwd file."
else
echo "the user 'jason' does not exist in the passwd file."
fi
echo -n "Are you sure you wish to remove '$file'?"
ready YN
if [ "$YN" = "y" -o "$YN" = "Y" ]
then
echo "Deleting '$file'..."
rm "$file"
else
echo "Aborted. '$file' not deleted."
fi
if [ "$(date +%Y)" -lt 2010 ]
then
echo "Still waiting for the Whistler Olympics."
fi
= while =
Format:
while ''pipeline''
do
''commands''
done
Executes ''commands'' once for each time that ''pipeline'' returns a true result (exit code of zero). Example:
!!!!!!!!! Need example !!!!!!!!!!
= for (list) =
for ''variable'' in ''list''
do
''commands''
done
Examples:
for COLOUR in red blue green
do
print "$COLOUR"
done
for FILE in /etc/*
do
if [ -x $FILE ]
then
echo "$FILE is executable"
fi
done
for MOUNT in $(mount|sed "/\//s/^.*on \([^ ]*\) .*$/\1/")
do
du -sx $MOUNT
done
= for (numeric) =
This is a C-style ''for'' loop:
for (( ''variable''=''start'' ; ''condition'' ; ''interation-action'' ))
do
''commands''
done
The value of ''variable'' is initially set to the integer value ''start'', and ''commands'' are executed repeatedly, performing ''iteraction-action'' each time until ''condition'' is no longer true. Note that this loop is performed in the [[BASH Math]] context, and therefore ''condition'' is written with symbols such as <, >, <=, and >= instead of -lt, -gt, -le, and ge.
Example:
for ((x=0; x<=10; x++))
do
echo $x
done
= case =
case ''expression'' in
''pattern1''<nowiki>[</nowiki>|''pattern1b''...<nowiki>]</nowiki>)
''commands1''
;;
<nowiki>[</nowiki>''pattern2''<nowiki>[</nowiki>|''pattern2b''...<nowiki>]</nowiki>)
''commands2''
;; ...<nowiki>]</nowiki>
esac
Executes the first group of commands for which the corresponding pattern(s) match the ''expression''. The matching is done using globbing rules.
Example:
read x
case "$x" in
y*|Y*) echo "Interpreting that as 'yes'" ;;
n*|N*) echo "Interpreting that as 'no'" ;;
*) echo "did you mean yes or no?!" ;;
esac
= if =
Format:
if ''pipeline''
then
''success-commands''
<nowiki>[</nowiki>elif ''pipeline2''
''else-if-commands''
<nowiki>]</nowiki>
<nowiki>[else</nowiki>
''alt-commands''
<nowiki>]</nowiki>
fi
Executes ''success-commands'' if ''pipeline'' returns an exit code of zero.
If ''success-commands'' returns a non-zero exit code and ''pipeline2'' returns an exit code of zero, executes ''else-if-commands''.
Otherwise, executes ''alt-commands''.
Examples:
if grep -q "jason" /etc/passwd
then
echo "the user 'jason' exists in the passwd file."
else
echo "the user 'jason' does not exist in the passwd file."
fi
echo -n "Are you sure you wish to remove '$file'?"
ready YN
if [ "$YN" = "y" -o "$YN" = "Y" ]
then
echo "Deleting '$file'..."
rm "$file"
else
echo "Aborted. '$file' not deleted."
fi
if [ "$(date +%Y)" -lt 2010 ]
then
echo "Still waiting for the Whistler Olympics."
fi
= while =
Format:
while ''pipeline''
do
''commands''
done
Executes ''commands'' once for each time that ''pipeline'' returns a true result (exit code of zero). Example:
!!!!!!!!! Need example !!!!!!!!!!
= for (list) =
for ''variable'' in ''list''
do
''commands''
done
Examples:
for COLOUR in red blue green
do
print "$COLOUR"
done
for FILE in /etc/*
do
if [ -x $FILE ]
then
echo "$FILE is executable"
fi
done
for MOUNT in $(mount|sed "/\//s/^.*on \([^ ]*\) .*$/\1/")
do
du -sx $MOUNT
done
= for (numeric) =
This is a C-style ''for'' loop:
for (( ''variable''=''start'' ; ''condition'' ; ''interation-action'' ))
do
''commands''
done
The value of ''variable'' is initially set to the integer value ''start'', and ''commands'' are executed repeatedly, performing ''iteraction-action'' each time until ''condition'' is no longer true. Note that this loop is performed in the [[BASH Math]] context, and therefore ''condition'' is written with symbols such as <, >, <=, and >= instead of -lt, -gt, -le, and ge.
Example:
for ((x=0; x<=10; x++))
do
echo $x
done
= case =
case ''expression'' in
''pattern1''<nowiki>[</nowiki>|''pattern1b''...<nowiki>]</nowiki>)
''commands1''
;;
<nowiki>[</nowiki>''pattern2''<nowiki>[</nowiki>|''pattern2b''...<nowiki>]</nowiki>)
''commands2''
;; ...<nowiki>]</nowiki>
esac
Executes the first group of commands for which the corresponding pattern(s) match the ''expression''. The matching is done using globbing rules.
Example:
read x
case "$x" in
y*|Y*) echo "Interpreting that as 'yes'" ;;
n*|N*) echo "Interpreting that as 'no'" ;;
*) echo "did you mean yes or no?!" ;;
esac
