Looking through files is done with the ls command under Linux, which is an abbreviation for list.

By default (meaning without parameters) the ls command shows the content in the current directory. It does hide elements starting with a dot though. These hidden elements can be shown by adding the -a parameter, which stands for all. If you want detailed information about the elements, add the -l parameter for long listing. You can also specify a file/directory which you want to examine, by just appending the path to the command.

$ ls      # shows files and directories
testdir  test

$ ls -a   # includes hidden ones
.  ..  testdir  test

$ ls -l   # detailed view
drwxr-xr-x 1 myuser p12345 0 Apr 13  2017 testdir
-rw-r--r-- 1 myuser p12345 4 Apr 13 11:55 test

$ ls /tmp/
allinea-USERNAME
ssh-6E553lWZCM
ssh-C6a754pJ1d
systemd-private-a4214393983d448fbdc689791806519c-ntpd.service-LrAgBP
tmp7CJZRA
yum_save_tx.2017-04-03.12-07.VCUowf.yumtx

$ ls -alh ~
drwxr-xr-x  5 myuser mygroup   45 Jan 30  2017 .allinea
-rw-------  1 myuser mygroup  21K May  3 17:14 .bash_history
-rw-r-----  1 myuser mygroup  231 Dec  2  2016 .bashrc
drwx------  1 myuser mygroup   76 Aug 22  2017 Simulation
drwx------  2 myuser mygroup   76 Dec 12  2016 .ssh

Moving through directories is done with the cd command, which stands for change directory.

The cd command can be called without any arguments, in which case it just switches to the home directory. Otherwise it takes a absolute (starting with a dash) or relative path as an argument and switches to that directory. The argument - (just a single dash) will cause cd to switch to the previous directory. This can be used to alternate between two directories without typing their path’s every time.

$ cd /bin   # go to an absolute directory

$ cd [~]    # go home

$ cd -      # go to previous directory

Copying and moving files and directories is done with the cp and mv commands, which stand for copy and move respectively.

Both commands take at least two parameters, which correspond to the <SOURCE> and <DESTINATION> files or directories. For cp to work with directories as a source, it needs the -r (recursive) or -a (archive) flag.

Beware of the pitfalls! you can overwrite data and therefor lose it, without getting any confirmation prompt! If in doubt use -i (interactive) flag.

$ mv old   new     # rename old to new

$ mv old   dir/    # move old into dir

$ mv file1 file2   # overwrite file2 with file1
                   # (BEWARE)

$ cp -i input input.bak   # input to input.bak

$ cp -i input backup/     # input into backup

$ cp -a dir1/ dir2        # exact copy of dir1

creating directories is done with the mkdir command, which stands for make directory.

The mkdir command takes an optional -p (parents) parameter and a path. When optional parameter is given, it will create all the ancestors of the specified directory aswell. Otherwise the command fails if the directory either exists already or its parent doesn’t exist either.

deleting directories is done with the rmdir command, which stands for remove directory.

This command removes the specified directory, but only if it’s already empty. it can also take an optional -p parameter, in which case it removes the specified directory and all the ancestors you included.

To look at everything

1. in your home directory
2. and nested up to three levels deep inside it
3. that ends in .txt
4. or starts with log_
5. and is an ordinary file
6. concatenated as one stream:

find \
  ~ \
  -maxdepth 3 \
  -iname "*.txt" \
  -or -iname "log_*" \
  -type f \
  -exec cat '{}' \; | less

find \
  ~ \
  -maxdepth 3 \
  -iname "*.txt" \
  -or -iname "log_*" \
  -type f \
  -exec cat '{}' +  | less

viewing is done by the less command:

concatenating is done by the cat command:

$ less file.txt      # exit with 'q'

$ less -R file.txt   # keep colors

$ cat file1 file2 | less

$ cat file

$ cat -A printable

$ cat -n numbered

$ echo "VSC is great" > file
$ cat file
VSC is great

$ echo "VSC is awesome" >> file
$ cat file
VSC is great
VSC is awesome

$ cat file | grep awesome
VSC is awesome

$ grep awesome file
VSC is awesome

viewing used space is done by the du (disk usage) command:

viewing free space is done by the df (disk free) command:

$ du -h file1 file2   # human readable output

$ du -s dir           # summarize

$ df -h       # human readable output

$ df -t nfs   # only list filesystems of a type

$ mv space.log space.log.bak

$ df -h | grep "lv12345\|lv54321" > space.log

$ cat space.log

nfs05.ib.cluster:/e/lv12345    200G  185G   16G  93% /home/lv12345
nfs04.ib.cluster:/e/lv54321   1000G  979G   22G  98% /home/lv54321

we do this often, let’s wrap it up!

$ mv space.log space.log.bak

$ df -h | grep "lv12345\|lv54321" > space.log

$ cat space.log

nfs05.ib.cluster:/e/lv12345    200G  185G   16G  93% /home/lv12345
nfs04.ib.cluster:/e/lv54321   1000G  979G   22G  98% /home/lv54321

we do this often, let’s wrap it up!

$ echo '#!/bin/bash' > spacelog.sh

$ echo 'mv space.log space.log.bak' >> spacelog.sh

$ echo 'df -h | grep "lv12345\|lv54321" > space.log' >> spacelog.sh

$ echo 'cat space.log' >> spacelog.sh

$ chmod +x spacelog.sh

$ ./spacelog.sh

sed (stream editor) and awk are powerful tools when working with the command line

$ mycommand | sed "..."

$ mycommand | awk '{...}'

Using sed and awk in action

Example script:

#!/bin/bash
 
mv space.log space.log.bak
df -h | grep "lv12345\|lv54321" > space.log
cat space.log

#!/bin/bash
 
mv space.log space.log.bak
df -h | grep "lv12345\|lv54321" > space.log
cat space.log | sed "s|/home/lv12345|ProjectA|" \
              | awk '{print $6, "free:", $4}' \
              | column -t

<HTML> <!– ### Sort and uniq

sort and uniq (unique) are used to sort and uniquify adjacent lines

–> </HTML>