Learning some commands makes Linux life easier

Redirecting inputs and outputs

It's about these two operator '<' and '>'. For example,

$ ls -l > fileList.txt

The output of this command is not printed on the screen, it is written to a file named fileList.txt.

cat command

Purpose of this command is equivalent to "type" command. You can view contents of a text file using cat command. Example given below,

$ cat fileList.txt total 36 drwxrwxrwx 4 ar root 512 Dec 1 16:45 HarvardPackages -rwxrwxrwx 1 ar root 1098 Dec 1 16:49 IS_OS161_v1.3.1.sh~ -rwxrwxrwx 1 ar root 1140 Dec 1 16:49 IS_OS161_v1.3.2.sh drwxrwxrwx 2 ar root 512 Dec 1 16:44 Package 1.4 -rwxrwxrwx 1 ar root 244 Dec 1 16:49 Scripting.txt -rwxrwxrwx 1 ar root 189 Dec 1 16:49 Scripting.txt~ drwxrwxrwx 12 ar root 512 Dec 1 16:47 cs161-binutils-1.4 drwxrwxrwx 6 ar root 512 Dec 1 16:48 cs161-gcc-1.4-2 drwxrwxrwx 14 ar root 512 Dec 1 16:44 cs161-gdb-1.4-2 -rw-r--r-- 1 ar other 0 Dec 26 20:03 fileList.txt -rwxrwxrwx 1 ar root 148 Dec 1 16:44 input.sh -rwxrwxrwx 1 ar root 294 Dec 1 16:49 install.sh~ -rwxrwxrwx 1 ar root 695 Dec 1 16:49 install_os161.sh -rwxrwxrwx 1 ar root 668 Dec 1 16:49 install_os161.sh~ drwxrwxrwx 10 ar root 512 Dec 1 16:49 os161-1.11 drwxrwxrwx 16 ar root 1024 Dec 1 16:49 sys161-1.12-2 -rwxrwxrwx 1 ar root 24 Dec 1 16:49 test2.txt~

grep

Very useful command. It is used to filter the outputs (pipes supported). If you don't understand the purpose in theory don't worry you will be able to understand from examples. If you give the command ls -a it will show like this,

$ ls -a total 44 drwxrwxrwx 9 ar root 512 Dec 26 20:03 . drwxrwxrwx 6 ar root 512 Dec 1 16:43 .. drwxrwxrwx 4 ar root 512 Dec 1 16:45 HarvardPackages -rwxrwxrwx 1 ar root 1098 Dec 1 16:49 IS_OS161_v1.3.1.sh~ -rwxrwxrwx 1 ar root 1140 Dec 1 16:49 IS_OS161_v1.3.2.sh drwxrwxrwx 2 ar root 512 Dec 1 16:44 Package 1.4 -rwxrwxrwx 1 ar root 244 Dec 1 16:49 Scripting.txt ........................................................................... ........................................................................... drwxrwxrwx 10 ar root 512 Dec 1 16:49 os161-1.11 drwxrwxrwx 16 ar root 1024 Dec 1 16:49 sys161-1.12-2 -rwxrwxrwx 1 ar root 24 Dec 1 16:49 test2.txt~

If the output was huge and wanted details about only the file whose name
contains Package. Then give the command like this:

$ ls -l | grep Package drwxrwxrwx 4 ar root 512 Dec 1 16:45 HarvardPackages drwxrwxrwx 2 ar root 512 Dec 1 16:44 Package 1.4

'|' This sign is called pipe which linked the output of first command to the second as input. You can search for files containing certain text string.

$ grep -r "textString" /path

Use -H switch to show line numbers. grep has many useful options learn them from manual ("$ man grep")

find

In case you know the name of a file but you don't know where it is then to find it's location use this command,

find /directoryname -name file.ext

which

If you apply a command but don't know from where it'll be executed or where the executable file resides? To view that location use this syntax,

which commandName

Example,

$ which gcc /usr/sfw/bin/gcc

It is the output for Solaris 10. Hence, your output can be different.

tar

An archive is a file containing compressed files and directories.

• creating an archive using tar command
  
  
  

  $ tar -cvf test.tar local.login local.profile .bashrc a local.login 1K a local.profile 1K a .bashrc 1K

  
  Why did we use v switch? Let's see the difference.
  
  
  

  $ tar -cf test.tar local.login local.profile .bashrc

  
  It means if v is included then tar displays information on every file it adds.
  
  To add a file in an existing archive use -r option(-f means next argument is
  the archive file name).
  
  
  

  $ tar -rf test.tar local.cshrc

  
  
• Extracting archive,
  If file extension contains tar.gz then syntax is,
       tar xzvf fileName.tar.gz
  
  If extension is tar.bz2
       tar xjvf fileName.tar.bz2
  
  if extension is only .tar then
       tar xvf fileName.tar.bz2

echo

This is the easiest command. You know about this. An example is,

$ echo "This line will be printed." This line will be printed.

zip and unzip

You can create zip files using zip command. Use following syntax.

$ zip ArchiveFileName.zip /path/dir_OR_file

To unzip a zip file (extract an zip archive) use following syntax

$ unzip ArchiveFileName.zip

To work with rar archives follow this post.