Linux Commands

Linux CLI Commands.md

• cat: concatenate files and print on the standard output
  • cat > a.txt: start a file creation
  • cat a.txt: show file content
  • cat a.txt b.txt: show files content respectively
  • cat a.txt b.txt > c.txt: create a file which contains a.txt and b.txt
• chmod: change file mode bits
  • chmod +x a.txt: All users and groups have the execute permission
  • chmod $u$g$o a.txt: Give specific user permission
    • $u -> current user permission number
    • $g -> current user's group permission number
    • $u -> others permission number
    • permission number can calculate with:
      • 0 -> no permission
      • 1 -> x (execute)
      • 2 -> w (write)
      • 4 -> r (read)
  • chmod 651 a.txt: it means user can write and read, group can read and execute, others can only execute.
• cd: change directory
  • cd a/: change directory to a (which is a directory in my current directory)
  • cd /opt/: change directory to opt (full path start with /)
  • cd ../:one directory up
  • cd ./: this directory
  • cd: return home directory for your user
• cp: copy files and directories
  • cp $source $destination: copy the file from source to destionation
  • cp -R a/ b/: copy directory(folder) to other folder. (-R = -r = --recursive)
• date: print or set the system date and time
• echo: display a line of text, args etc.
  • echo "string": it prints out "string"
  • echo $PATH: it prints $PATH variable's value
• grep: print lines matching a pattern
  • cat b.txt | grep q: the lines which contains q in b.txt.
  • cat b.txt | grep q$: the lines which ends with q in b.txt.
  • cat b.txt | grep ^q: the lines which starts with q in b.txt.
  • ! for regex usage you can only specify the -E(or -e): cat b.txt | grep -E q$.
• head: output the first part of files
  • head b.txt: first 10 lines of the b.txt (default)
  • head b.txt -n 4: first 4 lines of the b.txt
• ls: list directory contents
  • ls: list current directory contents (only general files ignore hidden files(which starts with .))
  • ls a/: list directory a's contents
  • ls -l: list current directory contents (long list format)
  • ls -a: list current directory all contents (do not ignore hidden files)
  • ls -la: all file in long list format
• more: file perusal filter for crt viewing
  • more b.txt: paginate the contents of the b.txt
  • cat b.txt | more: this also paginates
• less: opposite of more
• mkdir: make directories
  • mkdir NEWFOLDERNAME: create a folder(directory) name NEWFOLDERNAME
• mv: move (rename) files
  • mv $source $destination: move folder and files from source to destination (you can use it to rename a folder or file)
• pwd: print name of current/working directory
• rm: remove files or directories
  • rm b.txt: delete file named b.txt
  • rm -r a/: delete folder named a
• rmdir: remove empty directories
  • rmdir a/: delete directory if and only if the directory is empty
• export: set an environment variable
  • export VARIABLE_NAME="VALUE OF VARIABLE": it creates a variable named VARIABLE_NAME. (access name $VARIABLE_NAME)
• sort: sort lines of text filesq
• tail: output the last part of files
  • tail b.txt: last 10 lines of the b.txt (default)
  • tail -n 4 b.txt: last 4 lines of the b.txt
• tar: The GNU version of the tar archiving utility (tape archive)
  • tar -tvzf foo.tar.gz: list all files name in foo.tar.gz
  • tar -zcvf archive-name.tar.gz directory-name: create a tar.gz file from directory-name
  • tar -xvzf foo.tar.gz: uncompress all files in foo.tar.gz
    • -z: using gzip program
    • -x: extract (uncompress)
    • -c: create archive
    • -v: verbose (display progress while creating archive)
    • -f: archive file name
• ssh: OpenSSH SSH client (remote login program)
  • ssh eng1.mu.edu.tr: connect the eng1.mu.edu.tr server with SSH (it get your current username as a username in the server).
  • ssh mo.tercanli12@eng1.mu.edu.tr: connect the server with username: mo.tercanli12
• wc: print newline, word, and byte counts for each file
  • wc b.txt: prints out the number of Lines, Words, Characters
  • wc -l b.txt: only number of lines
  • wc -w b.txt: only number of words
  • wc -c b.txt: only number of character
• scp: secure copy (remote file copy program)
  • scp your_username@remotehost.edu:foobar.txt /some/local/directory: copy file from remote to local
  • scp foobar.txt your_username@remotehost.edu:/some/remote/directory: copy file from local to remote
• wget: The non-interactive network downloader.
  • wget $URL: download url content from $URL
  • wget $URL -O a.txt: download url content from $URL and save it as a.txt
• curl: transfer a URL
• find: search for files in a directory hierarchy
• man: an interface to the on-line reference manuals
  • man tar: manual page for tar
• sed: stream editor for filtering and transforming text
  • sed s/one/ONE/ < a.txt: it process the file a.txt and all one become ONE. (a.txt does not change)
• awk: pattern scanning and processing language