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This article deals with so-called core utilities on a GNU/Linux system, such as less, ls, and grep. The scope of this article includes, but is not limited to, those utilities included with the GNUpackage. What follows are various tips and tricks and other helpful information related to these utilities.
cat (catenate) is a standard Unix utility that concatenates and lists files.
- As cat is not a shell built-in, in many occasions you may find more convenient to use a redirection, for example in scripts, or if you care a lot about performance. In fact
< filedoes the same of
- To append multiple lines to a file a construct like this one is used:
$ cat << EOF >> path/file first line ... last line EOF
- If you need to cat file lines in reverse order, there is a utility called tac (cat reversed).
grep (from ed's g/re/p, global/regular expression/print) is a command line text search utility originally written for Unix. The grep command searches files or standard input globally for lines matching a given regular expression, and prints them to the program's standard output.
- Remember that grep handles files, so a construct like
$ cat file | grep patternis replaceable with
$ grep pattern file
- If you have to grep VCS source code, there is an optimized utility written in Perl and called official web site. . See the
Beyond aesthetics, grep's color output is immensely useful for learning regexp and grep's functionality.
To use the default colors for grep, write the following entry to your shell configuration file, e.g. if using Bash:
alias grep='grep --color=auto'
To include file line numbers in the output, add
alias grep='grep -n --color=auto'
The environment variable
GREP_COLORS may be used to specify different colors than the defaults.
ifconfig (interface configuration) is a system administration utility in Unix-like operating systems to configure, control, and query TCP/IP network interface parameters from a command line interface (CLI) or in system configuration scripts.
It is deprecated: the alternative is called ip.
less is a terminal pager program used to view the contents of a text file one screen at a time. Whilst similar to other pages such as more and pg, less offers a more advanced interface and complete feature-set.
Colored output through environment variables
Add the following lines to your shell configuration file:
export LESS=-R export LESS_TERMCAP_me=$(printf '\e[0m') export LESS_TERMCAP_se=$(printf '\e[0m') export LESS_TERMCAP_ue=$(printf '\e[0m') export LESS_TERMCAP_mb=$(printf '\e[1;32m') export LESS_TERMCAP_md=$(printf '\e[1;34m') export LESS_TERMCAP_us=$(printf '\e[1;32m') export LESS_TERMCAP_so=$(printf '\e[1;44;1m')
Change values as you like. References: ANSI escape code.
Colored output through wrappers
You can enable code syntax coloring in less. First, install, then add these lines to your shell configuration file:
export LESSOPEN="| /usr/bin/source-highlight-esc.sh %s" export LESS='-R '
Frequent users of the command line interface might want to install.
Users may now list the compressed files inside of an archive using their pager:
$ less compressed_file.tar.gz
==> use tar_file:contained_file to view a file in the archive -rw------- username/group 695 2008-01-04 19:24 compressed_file/content1 -rw------- username/group 43 2007-11-07 11:17 compressed_file/content2 compressed_file.tar.gz (END)
lesspipe also grants less the ability of interfacing with files other than archives, serving as an alternative for the specific command associated for that file-type (such as viewing HTML via).
Re-login after installing lesspipe in order to activate it, or source
Vim as alternative pager
Vim (visual editor improved) has a script to view the content of text files, compressed files, binaries, directories. Add the following line to your shell configuration file to use it as a pager:
ls (list) is a command to list files in Unix and Unix-like operating systems.
Colored output can be enabled with a simple alias. File
~/.bashrc should already have the following entry copied from
alias ls='ls --color=auto'
The next step will further enhance the colored ls output; for example, broken (orphan) symlinks will start showing in a red hue. Add the following to your shell configuration file:
eval $(dircolors -b)
man (manual page) is a form of online software documentation usually found on a Unix or Unix-like operating system. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts. See Man Pages.
mkdir (make directory) is a command to create directories. To create a directory and its whole hierarchy,
-p switch is used, if not a error is printed. As users are supposed to know what they want,
-p switch may be used as a default.
alias mkdir='mkdir -p -v'
-v switch make it verbose.
mv (move) is a command to move and rename files and directories. It can be very dangerous so it is prudent to limit its scope:
alias mv=' timeout 8 mv -iv'
This alias suspends mv after eight seconds, asks confirmation to delete three or more files, lists the operations in progress and does not store itself in the shell history file if the shell is configured to ignore space starting commands.
rm (remove) is a command to delete files and directories. It can be very dangerous so it is prudent to limit its scope:
alias rm=' timeout 3 rm -Iv --one-file-system'
This alias suspends rm after three seconds, asks confirmation to delete three or more files, lists the operations in progress, does not involve more than one file systems and does not store itself in the shell history file if the shell is configured to ignore space starting commands. Substitute
-i if you prefer to confirm even for one file.
sed (stream editor) is a Unix utility that parses and transforms text.
Here is a handy list of sed one-liners examples.
seq (sequence) is a utility for generating a sequence of numbers. Shell built-in alternatives are available, so it is good practice to use them as explained on Wikipedia.
shred is a command to securely delete files and directories. It can be very dangerous so it is prudent to limit its scope:
alias shred=' timeout 3 shred -v'
This alias suspends shred after three seconds, lists the operations in progress, and does not store itself in the shell history file if the shell is configured to ignore space starting commands.
Sudo (as superuser do) is a program for Unix-like computer operating systems that allows users to run programs with the security privileges of another user (normally the superuser, or root). See Sudo.