If statement without any brackets:
\n These are used to check the outcome of a command. It return the exist status of command executed after if.<\/p>\n
if grep -i oolala lyrics.txt
\nthen
\n echo “lyrics.txt file contains oolala”
\nelse
\n echo “lyrics.txt file doesn’t contain oolala”
\nfi <\/p>\n
if statement with []:
\nThese are used to check the file types and compare strings.<\/p>\n
if [ -z $variable ]
\nthen
\n echo “Variable is empty”
\nelse
\n echoo “Variable is not empty”
\nfi<\/p>\n
if statement with [[]]:
\nThese are used for the same purpose as [] but more versatile and doesn\u2019t give error when &&, ||, >, < are used within these brackets unlike [].\n\nif [[ \"$number1\" -eq \"$number2\" ]] \nthen\n echo \"numbers are equal\"\nelse\n echo \"numbers are not equal\"\nfi\n\nif statement with no \u201cif\u201d:\nThese are useful to evaluate a condition and take a single action.\n\n[ -f \"$filename\" ] || touch $filename # if $filename doesn't exist, it will touch that file\n[ -f \"$filename\" ] && rm $filename # if $filename exists, it will remove that file\n\nnested if statement:\nif [[ \"$fruitname\" == \"apple\" ]]\nthen\n echo \"Fruit is apple\"\nelif [[ \"$fruitname\" == \"mango\" ]] \nthen\n echo \"Fruit is mango\"\nelse\n echo \"Fruit can not be identified\"\nfi\n\nCompound if conditions\nThis is a combination of more than one test expression in if statement. Best explained with an example.\n\nnum1=10\nnum2=20\nif [ \"$num1\" -eq 10 ] && [ \"$num2\" -eq 20 ]\nthen\n echo \"Number test successful\" => It is successful because both numbers match their values
\nelse
\n echo “Number test failed”
\nfi
\nif [ “$num1” -eq 10 ] || [ “$num2” -eq 30 ]
\nthen
\n echo “Number test successful” => It is successful because num1 matches 10
\nelse
\n echo “Number test failed”
\nfi
\nif [ “$num1” -eq 10 -a “$num2” -eq 20 ]
\nthen
\n echo “Number test successful” => It is successful because both numbers match their values
\nelse
\n echo “Number test failed”
\nfi
\nif [ “$num1” -eq 30 -o “$num2” -eq 20 ]
\nthen
\n echo “Number test successful” => It is successful because num2 matches 20
\nelse
\n echo “Number test failed”
\nfi<\/p>\n
fruit1=apple
\nfruit2=mango
\nif [ “$fruit1” == apple ] && [ “$fruit2” == mango ]
\nthen
\n echo “String test successful” => It is successful because both strings match their values
\nelse
\n echo “String test unsuccessful”
\nfi<\/p>\n
Test Operators<\/p>\n
File test operators:
\n To be used as:-
\nif [ “operator” $filename ]; then<\/p>\n
-e : Filename exists
\n-d : Filename exists and is a directory
\n-f : Filename exists and is a regular file
\n-s : Filename exists and its size is greater than zero
\n-b : Filename exists and is a block device
\n-c : Filename exists and is a character device
\n-p : Filename exists and is a pipe
\n-L : Filename exists and is a symbolic Link
\n-S : Filename exists and is a socker
\n-g : setgid is set on filename
\n-u : setuid is set on filename
\n-k : sticky bit is set on filename
\n-r : user running the script has read permission on given file
\n-w : user running the script has write permission on given file
\n-x : user running the script has execute permission on given file
\n-O : user running the script is owner of given file
\n-G : user running the script has same group id as of the script
\nfile1 -nt file2 : File file1 is newer than file2
\nfile1 -ot file2 : File file1 is older than file2
\nfile1 -ef file2 : file1 and file2 are hard links to the same file<\/p>\n
String operators: = : strings are equal Numeric Operators: -eq : numbers are equal #! \/bin\/ksh<\/p>\n if [[ -s $FILE ]] ; then Reading from a file<\/p>\n for line in $(cat \/etc\/passwd) Iterate for a range<\/p>\n for number in {1..10} Loop for values given<\/p>\n for planet in earth mars saturn jupiter Loop for variable containing multiple values<\/p>\n planets=\u201dearth mars saturn jupiter pluto\u201d If statement without any brackets: These are used to check the outcome of a command. It return the exist status of command executed after if.<\/p>\n if grep -i oolala lyrics.txt then echo “lyrics.txt file contains oolala” else echo “lyrics.txt file doesn’t contain oolala” fi <\/p>\n if statement with []: These are used to check the […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[47],"tags":[],"_links":{"self":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/3355"}],"collection":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3355"}],"version-history":[{"count":3,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/3355\/revisions"}],"predecessor-version":[{"id":3358,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/3355\/revisions\/3358"}],"wp:attachment":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3355"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3355"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3355"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
\n To be used as:-
\n if [ “$string1”
\n== : strings are equal
\n!= : strings are not equal
\n< : string1 is less than string2 in ASCII order. \n if [[ \"string1\" < \"string2\" ]] or if [[ \"string1\" \\< \"string2\" ]\n> : string1 is more than string2 in ASCII order.
\n if [[ “string1” > “string2” ]] or if [[ “string1” \\> “string2” ]
\n-z : string is empty
\n-n : string is not empty<\/p>\n
\n To be used as:-
\nif [ “$number1”
\n-ne : numbers are not equal
\n-gt : number1 is greater than number2
\n-ge : number1 is greater than or equal to number2
\n-lt : number1 is less than number2
\n-le : number1 is less than or equal to number2
\n< : number1 is less than number2. To be used within (()) without the word \"if\". \n (( \"$num1\" < \"$num2\" ))\n<= : number1 is less than or equal to number2. To be used within (()) without the word \"if\". \n (( \"$num1\" <= \"$num2\" ))\n> : number1 is greater than number2. To be used within (()) without the word “if”.
\n (( “$num1” > “$num2” ))
\n>= : number1 is greater than or equal to number2. To be used within (()) without the word “if”.
\n (( “$num1” >= “$num2” ))<\/p>\n
\necho “$FILE has data.”
\nelse
\necho “$FILE is empty.”
\nfi ;<\/p>\n
\n do
\n echo $line
\n done<\/p>\n
\n do
\n echo \u201cCurrent number is $number\u201d
\ndone<\/p>\n
\n do
\n echo \u201cThe planet name is $planet\u201d
\ndone<\/p>\n
\nfor planet in $planets
\n do
\n echo \u201cThe planet name is $planet\u201d
\ndone<\/p>\n","protected":false},"excerpt":{"rendered":"