grep return 0 if no match
The actual answer to this question is to add || true to the end of the command, e.g.: echo thing | grep x || true This will still output a 0 return code.
grep
What flavour of regular expression is grep?
Default GNU grep behavior is to use a slightly flavorful variant on POSIX basic regular expressions, with a similarly tweaked species of POSIX extended regular expressions for egrep (usually an alias for grep -E). POSIX ERE is what PHP ereg() uses. GNU grep also claims to support grep -P for PCRE, by the way. So … Read more
How can I see many grep results page by page?
try grep YOUR_PATTERN_AND_OPTION YOUR_PATH | less or grep YOUR_PATTERN_AND_OPTION YOUR_PATH | more
grep: repetition-operator operand invalid
$ grep -Pio ‘(?<=heads\/)(.*?)(?=\n)’ text.txt # P option instead of E If you use GNU grep, you can use -P or –perl-regexp options. In case you are using OS X, you need to install GNU grep. $ brew install grep Due to recent changes, to use GNU grep on macOS you either have to prepend … Read more
How to always cut the PID from `ps aux` command?
-d ‘ ‘ means using a single space as delimiter. Since there’re 1 space before 2049 and 2 spaces before 12290, your command get them by -f 2 and -f 3. I recommend using ps aux | awk ‘{print $2}’ to get those pids. Or you can use tr to squeeze those spaces first ps … Read more
Ansible shell module returns error when grep results are empty
grep by design returns code 1 if the given string was not found. Ansible by design stops execution if the return code is different from 0. Your system is working properly. To prevent Ansible from stopping playbook execution on this error, you can: add ignore_errors: yes parameter to the task use failed_when: parameter with a … Read more
grep recursive filename matching (grep -ir “xyz” *.cpp) does not work
Grep will recurse through any directories you match with your glob pattern. (In your case, you probably do not have any directories that match the pattern “*.cpp”) You could explicitly specify them: grep -ir “xyz” *.cpp */*.cpp */*/*.cpp */*/*/*.cpp, etc. You can also use the –include option (see the example below) If you are using … Read more
ack misses results (vs. grep)
ack is peculiar in that it doesn’t have a blacklist of file types to ignore, but rather a whitelist of file types that it will search in. To quote from the man page: With no file selections, ack-grep only searches files of types that it recognizes. If you have a file called foo.wango, and ack-grep … Read more
How do you exclude symlinks in a grep?
Gnu grep v2.11-8 and on if invoked with -r excludes symlinks not specified on the command line and includes them when invoked with -R.
Read expression for grep from standard input
Use -f with a single dash to denote the standard input: $ echo Content | grep -f – notice.html <meta http-equiv=”Content-Type” content=”text/html; charset=ISO-8859-1″> … Note: This has been tested with GNU grep – I am not sure if it’s specified by POSIX.