Exit status. Every process returns an exit status ( or code) a code of 0 means the process ran successfully. A non-zero indicates an error. The exit status of the last command executed is available in $?.
$ cat bf1 who >/dev/null echo :$?: who | grep godzilla >/dev/null echo :$?: $ bf1 :0: :1:
Commands are run using the pipe |, ;, &, && or ||.
$ cat bf2 ls -ld [A-Z]*; who (ls -ld [A-F]*; who) >bfo cat bfo $ bf2 -rw------- 1 kochis 333 Jun 11 08:44 Cancelled.mail drwx------ 4 kochis 512 Jun 17 15:00 Mail drwxr-xr-x 2 kochis 512 Jun 19 08:38 News kochis console Jun 27 09:42 kochis ttyp0 Jun 27 09:42 (unix:0.0) kochis ttyp1 Jun 27 09:42 (unix:0.0) -rw------- 1 kochis 333 Jun 11 08:44 Cancelled.mail kochis console Jun 27 09:42 kochis ttyp0 Jun 27 09:42 (unix:0.0) kochis ttyp1 Jun 27 09:42 (unix:0.0)
$ cat bf3 ls -ld [A-Z]* & who $ bf3 -rw------- 1 kochis 333 Jun 11 08:44 Cancelled.mail drwx------ 4 kochis 512 Jun 17 15:00 Mail kochis console Jun 27 09:42 kochis ttyp0 Jun 27 09:42 (unix:0.0) kochis ttyp1 Jun 27 09:42 (unix:0.0) $ drwxr-xr-x 2 kochis 512 Jun 19 08:38 News
$ cat bf4 grep vacuum /usr/lib/spell/list && echo "good word" $ bf4 vacuum good word
$ cat bf5 grep $1 /usr/lib/spell/list || echo "not in dictionary" $ bf5 cochise not in dictionary
The test command is used to check conditions in the Bourne Shell.
The general format is :
test condition
[ condition ]
If the condition is true test return a zero (0) if the test fails it
returns a nonzero.
$ cat bf6 echo "strings" one="zip" echo example 1. test "$one" = zip echo :$?: echo example 2. one="zip " [ "$one" = zip ] echo :$?: echo example 3. test $one = zip echo :$?: echo example 4. one= [ $one = zip ] echo :$?: $
$ bf6 strings example 1. :0: example 2. :1: example 3. :0: example 4. bf6: test: argument expected $To check for inequality use !=
Strings may be check for null with -n (not null) or -z (null)
echo "strings" one= test -n "$one" echo example 1 :$?: [ -z "$one" ] echo example 2 :$?: $ bf7 strings example 1 :1: example 2 :0:
The integer operators are:
-eq equal -ge greater than or equal -le less than or equal -gt greater than -lt less than -ne not equal
[ $count -lt 20 ]
The file operators of test are:
-d file is a directory -f file is an ordinary file -r file is readable -s file has a nonzero length -w file is writable -x file is executable
[ -d $here ]
The logical operators are
-a and -o or
[ -d $here -a $count -lt 100 ]
The if statement is:
if command
then
command
...
fi
$ cat bf9 day=`date | tr ' ' ':' | cut -d: -f3` if [ "$day" -gt 15 ] then echo "second half of month, are you broke?" fi $ bf9 second half of month, are you broke?
The if else statement is:
if command
then
command
...
else
command
...
fi
$ cat bfa day=`date | tr ' ' ':' | cut -d: -f3` if [ "$day" -gt 15 ] then echo "second half of month, are you broke?" else echo "first half of month" fi
The elif (else if construct is):
if command
then
command
...
elif command
command
...
else
command
....
fi
$ cat bfb
month=`date "+%m"`
echo the month number is $month
if [ "$month" -eq 1 ]
then
echo January
elif [ "$month" -eq 2 ]
then
echo February
elif [ "$month" -eq 3 ]
then
echo March
elif [ "$month" -eq 4 ]
then
echo April
elif [ "$month" -eq 5 ]
then
echo May
elif [ "$month" -eq 6 ]
then
echo June
elif [ "$month" -eq 7 ]
then
echo July
elif [ "$month" -eq 8 ]
then
echo August
elif [ "$month" -eq 9 ]
then
echo September
elif [ "$month" -eq 10 ]
then
echo October
elif [ "$month" -eq 11 ]
then
echo November
else
echo December
fi
$ bfb
the month number is 06
June
Note the spacing is not important to the syntax. The preceding
script could be written as:
month=`date "+%m"` echo the month number is $month if [ "$month" -eq 1 ] then echo January elif [ "$month" -eq 2 ] then echo February elif [ "$month" -eq 3 ] then echo March elif [ "$month" -eq 4 ] then echo April elif [ "$month" -eq 5 ] then echo May elif [ "$month" -eq 6 ] then echo June elif [ "$month" -eq 7 ] then echo July elif [ "$month" -eq 8 ] then echo August elif [ "$month" -eq 9 ] then echo September elif [ "$month" -eq 10 ] then echo October elif [ "$month" -eq 11 ] then echo November else echo December fi
The exit command may be used to return to the shell whenever necessary. If a value is specified then that is the value associated with the command, else exit uses the exit status from the last command issued.
$ cat bfc1 #!/bin/sh if [ $1 -ge 1 -a $1 -le 12 ] then exit 0 else exit 1 fi
$ cat bfc2 #!/bin/sh if bfc1 $1 then echo ok else echo bad month fi
$ bfc2 10 ok $ bfc2 17 bad month
The case syntax is:
case word in pattern1) commands ;; pattern2) commands ;; esac
$ cat bfd month=$1 case "$month" in 1 ) echo January ;; 2 ) echo February ;; 3 ) echo March ;; 4 ) echo April ;; 5 ) echo May ;; 6 ) echo June ;; 7 ) echo July ;; 8 ) echo August ;; 9 ) echo September ;; 10) echo October ;; 11) echo November ;; 12) echo December ;; esac $ bfd 4 April $ bfd 10 October
Case uses the same meta characters as file name expansion in specifying a pattern. * which can match anything is used as a default case.
$ cat bfe
month=$1
case "$month"
in
[Jj]an* ) echo January ;;
[Ff]eb* ) echo February ;;
[Mm]ar* ) echo March ;;
[Aa]pr* ) echo April ;;
[Mm]ay ) echo May ;;
[Jj]un* ) echo June ;;
[Jj]ul* ) echo July ;;
[Aa]ug* ) echo August ;;
[Ss]ep* ) echo September ;;
[Oo]ct* ) echo October ;;
[Nn]ov* ) echo November ;;
[Dd]ec* ) echo December ;;
*) echo not valid input ;;
esac
$ bfe jan
January
$ bfe Jan
January
$ bfe Augu
August
$ bfe junk
June
$ bfe fly
not valid input
Alternate patterns may be selected using the | (or) in the pattern selection.
$ cat bff
month=$1
case "$month"
in
2 ) echo 28 or 29 Days ;;
4 | 6 | 9 | 11 ) echo 30 Days ;;
[13578] | 1[02] ) echo 31 days ;;
*) echo not valid input ;;
esac
$
$ bff 2
28 or 29 Days
$ bff 6
30 Days
$ bff 10
31 days
$ bff 7
31 days
$ bff 13
not valid input
$
The null statement : does nothing , but may be useful for certain constructs.
$ cat bfg if grep $1 /usr/dict/words >/dev/null then : else echo spelling is terrible fi $ bfg monkey $ bfg mankey spelling is terrible