In last article, we discussed out Bash Environment Variables which always play an important role in Bash Shell Scripting and here in this article, we listed out all Bash External Variables which you can use while doing Bash Programming.

External programs are often used within shell scripts; there are a few builtin commands ( echo , which , and test are commonly builtin), but many useful commands are actually Unix utilities, such as tr , grep , expr and cut . The backtick (`)is also often associated with external commands.

bzip2Compression using the Burrows-Wheeler block sorting text compression algorithm and Huffman coding.
catList the contents of the specified file.
chageChange the password expiration date for the specified system user account.
chfnChange the specified user account’s comment information.
chgrpChange the default group of the specified file or directory.
chmodChange system security permissions for the specified file or directory.
chownChange the default owner of the specified file or directory.
chpasswdReads a file of login name and password pairs and updates the passwords.
chshChange the specified user account’s default shell.
compressOriginal Unix file compression utility.
cpCopy the specified files to an alternate location.
dfDisplay current disk space statistics for all mounted devices.
duDisplay disk usage statistics for the specified filepath.
fileView the file type of the specified file.
fingerDisplay information about user accounts on the Linux system or a remote system.
grepSearch a file for the specified text string.
groupaddCreate a new system group.
groupmodModify an existing system group.
gzipThe GNU Project’s compression using Lempel-Ziv compression.
headDisplay the first portion of the specified file’s contents.
killallSend a system signal to a running process based on process name.
lessAdvanced viewing of file contents.
linkCreate a link to a file using an alias name.
lsList directory contents.
mkdirCreate the specified directory under the current directory.
moreList the contents of the specified file, pausing after each screen of data.
mountDisplay or mount disk devices into the virtual file system.
passwdChange the password for a system user account.
psDisplay information about the running processes on the system.
pwdDisplay the current directory.
mvRename a file.
rmDelete the specified file.
rmdirDelete the specified directory.
sortOrganize data in a data file based on the specified order.
statView the file statistics of the specified file.
tailDisplay the last portion of the specified file’s contents.
tarArchive data and directories into a single file.
touchCreate a new empty file, or update the timestamp on an existing file.
umountRemove a mounted disk device from the virtual file system.
useraddCreate a new system user account.
userdelRemove an existing system user account.
usermodModify an existing system user account.
zipUnix version of the Windows PKZIP program.