shell

Shell Script Syntax Error: Unexpected End of File

by

Edit: Note that the original post has been edited since this answer was written and has been reformatted. You should look at the history to see the original formatting to understand the context for this answer. This error occurs often when you have mismatched structure – that is, you do not have matching double quotes, … Read more

How to check if a variable is set in Bash?

by

(Usually) The right way where ${var+x} is a parameter expansion which evaluates to nothing if var is unset, and substitutes the string x otherwise. Quotes Digression Quotes can be omitted (so we can say ${var+x} instead of “${var+x}”) because this syntax & usage guarantees this will only expand to something that does not require quotes (since it either expands to x (which contains no word breaks so it … Read more

Replace one substring for another string in shell script

by

To replace the first occurrence of a pattern with a given string, use ${parameter/pattern/string}: To replace all occurrences, use ${parameter//pattern/string}: (This is documented in the Bash Reference Manual, §3.5.3 “Shell Parameter Expansion”.) Note that this feature is not specified by POSIX — it’s a Bash extension — so not all Unix shells implement it. For the relevant POSIX documentation, see The Open Group Technical … Read more

How can I declare and use Boolean variables in a shell script?

by

Revised Answer (Feb 12, 2014) Original Answer Caveats: https://stackoverflow.com/a/21210966/89391 From: Using boolean variables in Bash The reason the original answer is included here is because the comments before the revision on Feb 12, 2014 pertain only to the original answer, and many of the comments are wrong when associated with the revised answer. For example, Dennis Williamson’s … Read more