shell string comparison tests
\nHere are the operators for performing string comparison tests:<\/p>\n
s1 Test if s1 is not the empty string
\ns1 = s2 Test if s1 equals s2
\ns1 != s2 Test if s1 is not equal to s2
\n-n s1 Test if s1 has non-zero size
\n-z s1 Test if s1 has zero size
\nHere’s an example of how to see if two strings are equal:<\/p>\n
if [ $foo = $bar ]
\nthen
\n # do something
\nfi
\nThis script echoes TRUE:<\/p>\n
s1=<\/p>\n
if [ -n $s1 ]
\nthen
\n echo “TRUE”
\nelse
\n echo “FALSE”
\nfi
\nThis script echoes FALSE:<\/p>\n
s1=bar<\/p>\n
if [ -z “$s1” ]
\nthen
\n echo “TRUE”
\nelse
\n echo “FALSE”
\nfi<\/p>\n
Linux shell script math\/number equality tests
\nHere’s how you perform math\/number\/arithmetic tests using the Bourne and Bash shells:<\/p>\n
n1 -eq n2 Test if n1 equals n2
\nn1 -ne n2 Test if n1 is not equal to n2
\nn1 -lt n2 Test if n1 is less than n2
\nn1 -le n2 Test if n1 is less than or equal to n2
\nn1 -gt n2 Test if n1 is greater than n2
\nn1 -ge n2 Test if n1 is greater than or equal to n2
\nHere’s an example of how to test whether two numbers are equal:<\/p>\n
if [ $n1 -eq $n2 ]
\nthen
\n # do something
\nfi
\nLinux shell boolean and\/or\/not operators
\nThe following boolean and\/or\/not operators can also be used in your tests:<\/p>\n
-a and
\n-o or
\n! not
\nHere’s an example of how to test perform a test using the and operator:<\/p>\n
if [ $num -gt 0 -a $num -lt 10 ]
\nthen
\n # do something here
\nfi<\/p>\n
Linux shell script math\/number equality tests
\nHere’s how you perform math\/number\/arithmetic tests using the Bourne and Bash shells:<\/p>\n
n1 -eq n2 Test if n1 equals n2
\nn1 -ne n2 Test if n1 is not equal to n2
\nn1 -lt n2 Test if n1 is less than n2
\nn1 -le n2 Test if n1 is less than or equal to n2
\nn1 -gt n2 Test if n1 is greater than n2
\nn1 -ge n2 Test if n1 is greater than or equal to n2
\nHere’s an example of how to test whether two numbers are equal:<\/p>\n
if [ $n1 -eq $n2 ]
\nthen
\n # do something
\nfi
\nLinux shell boolean and\/or\/not operators
\nThe following boolean and\/or\/not operators can also be used in your tests:<\/p>\n
-a and
\n-o or
\n! not
\nHere’s an example of how to test perform a test using the and operator:<\/p>\n
if [ $num -gt 0 -a $num -lt 10 ]
\nthen
\n # do something here
\nfi<\/p>\n
a=5
\nb=20<\/p>\n
if test \\( $a -gt 0 -a $a -lt 10 \\) -o \\( $b -gt 0 -a $b -lt 20 \\)
\nthen
\n echo “TRUE”
\nelse
\n echo “FALSE”
\nfi
\nThat script echoes “TRUE”.<\/p>\n
Linux Bourne shell if, then, else, else if (elif) syntax
\nOne thing that varies from one programming language to another is the if \/ then \/ else \/ else if \/ elseif syntax. In the case of the Bourne shell, the “else if” keyword is actually “elif”, so a sample Bourne shell if then else if statement looks like this: <\/p>\n
if [ -e ‘foo’ ]
\nthen
\n echo “if was true”
\nelif [ -e ‘bar’ ]
\nthen
\n echo “elif was true”
\nelse
\n echo “came down to else”
\nfi<\/p>\n
Linux Bourne shell arithmetic
\nIn the Bourne shell math\/arithmetic is performed using the expr command, like this:<\/p>\n
sum=`expr $foo + $bar`
\nhalf=`expr $foo \/ 2`
\ntimes=`expr $foo \\* 2`<\/p>\n
# increment a counter
\n(( count++ ))
\nNote that you can’t have any spaces before or after the equal sign in those (or any) shell script assignment statements.<\/p>\n
A few other common Linux shell tricks
\nHere are a few other tricks\/techniques you will often see in Unix shell scripts:<\/p>\n
cmd1 && cmd2 Run cmd1; if it returns 0 (success), run cmd2
\ncmd1 || cmd2 Run cmd1; if it returns non-zero, run cmd2
\ncmd1 & cmd2 Run cmd1 and also cmd2
\n(ls -1) Run the command “ls -1” in a subshell<\/p>\n","protected":false},"excerpt":{"rendered":"
shell string comparison tests Here are the operators for performing string comparison tests:<\/p>\n
s1 Test if s1 is not the empty string s1 = s2 Test if s1 equals s2 s1 != s2 Test if s1 is not equal to s2 -n s1 Test if s1 has non-zero size -z s1 Test if s1 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[47],"tags":[],"_links":{"self":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/3413"}],"collection":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3413"}],"version-history":[{"count":1,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/3413\/revisions"}],"predecessor-version":[{"id":3414,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/3413\/revisions\/3414"}],"wp:attachment":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3413"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3413"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3413"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}