Shell Commands

Aug 8, 2021

:TODO: Clean up!

Setting default shell on linux:

• edit /etc/passwd/
• chsh

popd and pushd

• can use to create a directory ‘stack’
• pushd pushes the new directory to the stack, e.g., pushd ~/directory/another/andanother/
• then popd takes you back to the previous directory in the stack.
• popd +0 prints the stack (current directory first)
• popd +1 takes you to second directory in stack.

Exclamation mark !

• double exclamation !! re-run previous command
• exclamation plus number !500 run the ‘500th’ command from history
• exclamation plus a few characters !pa runs the recent command matching that pacman -Sy or whatever
• any of the above followed by colon ‘p’ !!:p prints the command instead of running it.
• exclamation with dollar sign !$ use argument of previous command.
  • E.g., say you create a file touch filename then, if you run vim !$ it will open that file in vim. Useful for very long filenames/arguments.
  • The $ represents the last argument of previous command. For example: ping google.com -c 4
    • echo !$ will print 4
    • echo !^ will print the first argument instead (google.com)
    • echo !* will print all the arguments (google.com -c 4)
  • to get a specific number argument, you first ‘select’ the command, then use colon+number. E.g.:
    • ping google.com -c 4
    • echo !!:2 returns -c if it was the previously run command. Alternatively, use !pi, !389 (the history number), etc.
    • Also, you can use ranges: echo !!:2-4
  • Also, you can ‘find and replace’ text in a command using ^ e.g.,
    • Say you run ping googl.com -c 4
    • You can correct the error in ‘googl’ with ^googl^google this automatically re-runs the command.

Tail

tail -n +1 file1.txt file2.txt file3.txt

Inserts filename with output

less +F ...

start less at the end of the file (for bigger files) you can also do shift + f to take to the end (not great on large files)

Find & Replace in Multiple Files

• grep -rl "old_string" . | xargs sed -i 's/old_string/new_string/g'

What is happening:

grep -rl: search recursively, and only print the files that contain “old_string” xargs: take the output of the grep command and make it the input of the next command (ie, the sed command) sed -i ‘s/old_string/new_string/g’: search and replace, within each file, old_string by new_string

Less - Exclude Lines from View

Once your file is open in `less` (or `journalctl`) press the following keys:

• `&`
• `!`
• `your-exclude-keyword`

Ampersand opens the pattern matching mode, exclamation mark tells `less` to exclude the following part, and then you enter your search term.

Shuf - shuffle

-o output (to file, for example)

Sort - sort

sorts alphabetically, use -n flag for numeric sorting. -r for reverse order -f ignore case Can use field separators. e.g.:

sort -t : -k 3n /etc/passwd
# sort using colon as delimiter, using 3rd column.

-u unique sorting - only sort unique lines. -o output (to file, for example) -R random sorting, but groups identical keys

Uniq - unique

Usually used in conjunction with sort. Removes duplicated lines. -u only return unique lines -d only return duplicated lines -c provide ‘count’ for how many times lines occur

Search and Replace within multiple files (alternative)

I used this to replace all the footer email links in the blog directory. Seemed to work perfectly. The section included with find makes sure to skip the git directory.

find . \( -type d -name .git -prune \) -o -type f -print0 | xargs -0 sed -i 's/mailto\:eoin\@spool\-five\.com/mailto\:eoincarney0\@gmail\.com/g'

Processes

• kill (process id)
• pgrep
• pstree
• setsid - spawn a detached child process