IT/Software/Command Line

Welcome to the dark world where most IT people live

• This is a gui free world
  • If you don't know what a gui is please quietly close the page and go buy a slurpee
  • If you don't know what a slurpee is we feel sorry for you.

Basic Commands

Find

This will help you find files and/or folders. Its power is amazing. It is often used in conjunction with commands. First find something and then do something.

find directory -user username

Directory is relative unless you specify absolute

Example: This will find all files and directories in the current directory AND recursively. Then it will touch the file changing its mtime and for most computers that is the timestamp that is read. Nextcloud will not accept old timestamps and so we have to use this command to clean things up. Lots of great "find" stuff here.

find . -exec touch {} \;

for some more security you can

find . -execdir touch '{}' \;

-execdir runs each command from the directory in which the find result is located. [the curly brace pair] should be quoted (for example, '{}') to protect it from interpretation by shells".

Changing Ownership

There are many ways to do this. Half of them may be more clever.

sudo chown walt:walt /path/to/filename

This will make the file filename belong to the user walt and the group walt. Usually we change the group and user at the same time.

OR

sudo chown user:group /path/to/directory/

This changes only the directory to user and group specified

Adding the -R flag after the chown will recurse into directories and files.

sudo chown -R . . .

• We are not sure why the capital r is needed in some cases. But it is here.

Changing Permissions

This is very similar except we use chmod instead of chown

sudo chmod 644 /path/to/file or path/to/directory/

Adding the -R flag does the same as above.

Change all files recursively to 644

find /var/www/html/moodlecnx/ -type f -exec chmod 644 {} \;

Change all directories recursively to 755

find /var/www/html/moodlecnx/ -type d -exec chmod 755 {} \;

you may need a "sudo" in front of chmod depending on where you are working.

Make a text file of the filenames in a directory

find -maxdepth 1 -type f ! -name flist.txt -printf  "%P\n" > flist.txt

Command information:

• -maxdepth: Don't search for files below folders of one level down.
• type f: Search for only files
• -printf "%P\n": Print the names only and on separate lines
• > flist.txt: Store those names (using output redirection) in a file to be created on the fly called `flist.txt
• ! -name flist.txt: Skips the name of the output file from the generated list

Make Directory

mkdir nameOfFolder

sudo mkdir name1 name2 nameX

mkdir -p /Path/newFolder

Mount and Unmount

iso files

sudo mkdir /mnt/iso

sudo mount -o loop Win10_2004_English_x64.iso  /mnt/iso

Symlinks

This allows you to click on a folder or directory and actually end up somewhere else.

For example if a user can't figure out how to get to the Documents folder from Dolphin.
ln -s /real/file/or/folder/path /path/to/link

The link can't already exist.

the path can be a file or directory.

Delete all files in folder tree

This will find all files under the parent directory(absolute) and recursively delete them.

It will not delete hidden files.

find  ~/msgcnxFiles/Teacher/Science/Biology/For\ Upload/ -type f -delete

zip Multiple Files with Date

zip -r path/from/here/"trial-$(date +"%Y-%m-%d")" Folder1 Folder2 Folder3

-r recurse into directories

You are adding the date command into the filename.

Then list all the wanted folders.

Note: The command is relative. It knows the folder you are in. You can specify all paths relative to the current folder or start with a / and you now have absolute referencing.

Delete files older than a specified time

find /home/walt/.config/Nextcloud/logs -name '*.gz' -type f -mmin +240 -exec rm {} \;

The above command will delete all files older than 240 minutes

You can change to -mtime +7 for older than 7 days.

Printing

lp is the classic

lp filename will print the file to the default printer with the default settings

lp -n 3 /path/*.pdf

Much time has been invested in learning this.

Make sure you install the printer correctly or you will get strange errors.

Stay away from "driverless" if you can.

List the default destination

lpstat -d

List the available printers

lpstat -d -p

List all jobs

lpstat -o

Cancel all jobs and delete them.

cancel -a -x

Print Portrait two sided.

lp -o sides=two-sided-long-edge

3 copies of any pdf file in that path.

-P page-list Specifies pages  to  print  in  the  document.   The  list  can contain a list of numbers and ranges (#-#) separated by commas, e.g.,

            "1,3-5,16".  The page numbers refer to the output pages and not the document's original pages

Print a directory

find  -name "*Test.*" -exec lp -o sides=two-sided-long-edge {} \;

Rename

• This function has many many options. We can only begin here.
• Below is an example where we prepend a 0 onto file names so that they order correctly on all OSes
• This works in the current working directory

rename -e 's/\d+/sprintf("%02d",$&)/e' -- *.jpg

Kill

• This function has many many options. We can only begin here.

Find the process id (pid) you want to kill and kill it.

kill -9 3567

If you know the name you can kill by name.

killall -9 vlc