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15. Quick Reference
This is a quick reference guide to the meaning of some of the less easily
guessed commands and codes.
Command
Description
Example
&
Run the previous command in the background
ls &
&&
Logical AND
if [ "$foo" -ge "0" ] && [ "$foo" -le "9"]
||
Logical OR
if [ "$foo" -lt "0" ] || [ "$foo" -gt "9" ] (not in Bourne shell)
^
Start of line
grep "^foo"
$
End of line
grep "foo$"
=
String equality (cf. -eq)
if [ "$foo" = "bar" ]
!
Logical NOT
if [ "$foo" != "bar" ]
$$
PID of current shell
echo "my PID = $$"
$!
PID of last background command
ls & echo "PID of ls = $!"
$?
exit status of last command
ls ; echo "ls returned code $?"
$0
Name of current command (as called)
echo "I am $0"
$1
Name of current command's first parameter
echo "My first argument is $1"
$9
Name of current command's ninth parameter
echo "My ninth argument is $9"
$@
All of current command's parameters (preserving whitespace and quoting)
echo "My arguments are $@"
$*
All of current command's parameters (not preserving whitespace and quoting)
My new 564-page book, Shell Scripting, published by Wiley, is on sale now. Please click "Like" on the left if you are on Facebook, or just click here to get the book.
