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2 Common Unix Commands

While there are hundreds of Unix commands, fortunately it is not necessary to know all of them.  In fact, one can achieve a significant level of productivity knowing just a couple of dozen.  Here are some of the most common and useful commands.

All commands are case sensitive.

Spaces are a BIG DEAL in Unix

When issuing commands, in order for Unix to tell when a command finishes and when parameters and file names start and end, every item (or token) on a command line must be separated by whitespace (one or more space characters).  One of the most common causes of frustration is failure to put whitepace between items on the command line, or putting whitespace where it should not be.

Just as in English, there is a big difference in meaning between “no table” and “notable”, so is the case in Unix.


ls /etc




Unix commands are a single word requesting an action.  Sometimes the action is standalone, but most actions are applied to some object like a file or directory.  At the point in the command where it expects the name of a file, say, this is where you specify the file in the form of an absolute or relative reference as described in the previous chapter.


What does it do?

Example usage

list directory contents List files (and directories) in my current directory


List files in top level etc directory

ls /etc

List all files beginning with g in the current directory. (The * is a wildcard.)

ls g*

List and give details about files in the current directory

ls -l

List all files including hidden files (those having a name beginning with a period character) in the current directory

ls -a


concatenate files and print on the standard output show contents of file report (in current directory)

cat report

show contents of files chapter1 and chapter2

cat chapter1 chapter2


output the first part of files show the first few lines of file longfile

head longfile


output the last part of files show the last few lines of file logfile

tail logfile


copy files and directories copy file report to report_v2 in the work directory

cp report work/report_v2


move (rename) files rename file report to presentation

mv report presentation

move file mydata to yourdata one level up

mv mydata ../yourdata


remove files (permanent) delete file report in current directory

rm report

Caution:  There is no recycling bin in Unix.  You should consider all deletions as permanent.  Exercise care when using wildcards (e.g. *).

change the working directory change directory to work directory (one level down)

cd work

change directory to /bin directory

cd /bin

change directory to parent (one level up)

cd ..

change directory to home directory of user ahmed

cd ~ahmed


print name of current/working directory Are you lost?



make directories create new directory called unix_exercises in the current directory

mkdir unix_exercises


remove empty directories remove (permanently delete) the directory unix_exercises from current directory

rmdir unix_exercises


show who is logged on display who else is logged in right now



print effective userid display one’s one userid (short login name)



print the system date and time
an interface to the on-line reference manuals display the manual entry for the ls command

man ls

Not sure of what command to look for?  Try a keyword search.  Display all commands pertaining to “directory”

man -k directory




Key Takeaways

  • Spaces are a BIG DEAL in Unix:  They are needed between commands, parameters, and filenames.
  • All commands are case-sensitive (usually all lowercase)

More Key Takeaways

  • Command options (e.g. -l, or -d, etc.) are specific to the command.  For example, while both the ls and and cp command both have a “-l” option, the option means different things in each command.  Command options are not mix and match.
  • Command options may be listed separately or combined.  The following are equivalent:
    • ls -ld
    • ls -l -d


More Unix Commands

All the commands below require some sort of input, typically a file, but the commands do not modify the input file.  The outputs will contain portions of the input files, but the input files are never changed.



What does it do?

Example usage

Print selected parts of lines from each FILE to standard output. display columns 1-10 and 20-23 of myfile

cut -c1-10,20-23 myfile

display the 3rd and 5th fields of the /etc/passwd file

cut -f3,5 -d: /etc/passwd


merge lines of files

If cat joins vertically, think of paste as a horizontal version of cat.

display file1, file2, and file3 side-by-side

paste file1 file2 file3


print newline, word, and byte counts for each file display the number of lines, words, and characters for the file chapter3

wc chapter3

display only the number of lines

wc -l chapter3


print lines matching a pattern display lines matching the string Total in the file sales

grep Total sales


sort lines of text files display a sorted version of the file namelist

sort namelist





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