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I would like to check if a string begins with "node" e.g. "node001". Something like
if [ $HOST == user* ] then echo yes fi How can I do it correctly?
I further need to combine expressions to check if HOST is either "user1" or begins with "node"
if [ [[ $HOST == user1 ]] -o [[ $HOST == node* ]] ]; then echo yes fi > > > -bash: [: too many arguments How can I do it correctly?
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We can use the double equals ( == ) comparison operator in bash, to check if a string starts with another substring. In the above code, if a $name variable starts with ru then the output is “true” otherwise it returns “false”.
To check if a string contains a substring in Bash, use comparison operator == with the substring surrounded by * wildcards.
Using Regex Operator Another option to determine whether a specified substring occurs within a string is to use the regex operator =~ . When this operator is used, the right string is considered as a regular expression. The period followed by an asterisk .
To access the first character of a string, we can use the (substring) parameter expansion syntax ${str:position:length} in the Bash shell. position: The starting position of a string extraction.
This snippet on the Advanced Bash Scripting Guide says:
# The == comparison operator behaves differently within a double-brackets # test than within single brackets. [[ $a == z* ]] # True if $a starts with a "z" (wildcard matching). [[ $a == "z*" ]] # True if $a is equal to z* (literal matching). So you had it nearly correct; you needed double brackets, not single brackets.
With regards to your second question, you can write it this way:
HOST=user1 if [[ $HOST == user1 ]] || [[ $HOST == node* ]] ; then echo yes1 fi HOST=node001 if [[ $HOST == user1 ]] || [[ $HOST == node* ]] ; then echo yes2 fi Which will echo
yes1 yes2 Bash's if syntax is hard to get used to (IMO).
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