Commands by Tomofumi (1)

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commandlinefu.com is the place to record those command-line gems that you return to again and again. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.

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Calculate days on which Friday the 13th occurs (inspired from the work of the user justsomeguy)
Friday is the 5th day of the week, monday is the 1st. Output may be affected by locale.

See why a program can't seem to access a file
Sometimes a program refuses to read a file and you're not sure why. You may have display_errors turned off for PHP or something. In this example, fopen('/var/www/test/foo.txt') was called but doesn't have read access to foo.txt. Strace can tell you what went wrong. E.g., if php doesn't have read access to the file, strace will say "EACCESS (Permission denied)". Or, if the file path you gave doesn't exist, strace will say "ENOENT (No such file or directory)", etc. This works for any program you can run from the command-line, e.g., strace python myapp.py -e open,access... Note: the above command uses php-cli, not mod_php, which is a different SAPI with diff configs, etc.

Pass TAB as field separator to sort, join, cut, etc.
Use this BASH trick to create a variable containing the TAB character and pass it as the argument to sort, join, cut and other commands which don't understand the \t notation. $ sort -t $'\t' ... $ join -t $'\t' ... $ cut -d $'\t' ...

Recursively grep thorugh directory for string in file.
-R, -r, --recursive Read all files under each directory, recursively; this is equivalent to the -d recurse option.

grab all commandlinefu shell functions into a single file, suitable for sourcing.
Much simpler but not as many features as the alternative.

Read just the IP address of a device

Convert files from DOS line endings to UNIX line endings
This method will also convert mac line endings.

Get a quick list of all user and group owners of files and dirs under the cwd.
find -printf '%u\n' | sort | uniq #just users find -printf '%g\n' | sort | uniq #just groups

Show a prettified list of nearby wireless APs

Android PNG screenshot
Works with *rooted* Android devices. 400x800 are the screen dimensions of a typical handheld smartphone.

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