======================================================================
Title:       Shell Commands
Date:        2021-08-08
Tags:        box3
Link:        https://spool-five.com/box3/20210808t000002--shell-commands__box3/
Word Count:  622
======================================================================



: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