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UNIX

Resources

Table of Contents

Find

  • find dir -type f Find all files in the directory
  • find dir -type d File all directories within this directory
  • find dir -name “a*.mp3” -print0 Find all files/directory with name like a***.mp3
  • find dir -type f -name “a*.txt” Find all files (recursively) with name like a***.txt
  • find dir -type f -print0 | xargs -0 grep -l "word" List file names with matching word
  • find dir -type f -print0 | xargs -0 mv -t Move all files from dir tree into single directory

Search

  • grep “word” file All matching lines in the file
  • grep -i “word” file All matching lines - Ignore case
  • grep -r “word” dir All matching lines in (recursively) all files or directory
  • grep -c “word” file Count of matching lines
  • grep “word” file | wc -l Count of matching lines
  • grep -v “word” file | wc -l Count of non-matching lines
  • grep -o -w “word” file | wc -w Word count
  • grep -l -r “word” dir List file names with matching word
  • find dir -type f -print0 | xargs -0 grep -l "word" List file names with matching word

Processes

  • nohup program.sh > mylog.txt 2>&1 &
    • & starts process as child process in the background
    • nohup Ctrl-C or terminating session sends kill signal to all child processes, nohup catches and ignores it
    • > redirect output (from left/source to right/target)
    • 2 error stream
    • 1 output stream
    • 2>&1 append all errors to output
  • top Check CPU and memory consumption
  • kill -9 processId kill the process with that pid
  • kill -3 processId for a JVM process, will write thread dump to output stream
  • ps -ef | grep word find process with matching word
  • echo $? print output of last process

File permissions

  • chmod file Change
  • chmod +x file Add execute permission
  • chmod +w file Add write permission
  • chmod +r file Add read permission
  • chmod 755 file Change permission
  • chmod -R 755 dir Change permission recursively
  • chmod g+w file Add write permission at group level
  • Numbers: 1=x, 2=w, 3=w+x, 4=r, 5=r+x, 6=r+w, 7=r+w+x
  • References: u=user, g=group, o=others, a=all

List files

  • ls list files in this directory
  • ls -ltr list files in this directory with more details and in reverse chronological order
  • ls -ltra same as above + list hidden files (names starting with .)
  • ls -ltr | grep "^l" Lists all symlinks (ls -ltr lists symlinks with l as first character of output)

Symlinks

  • Symbolic or soft links. Pointer to a file.
  • ln -s /java/jdk7 jdk create symlink jdk which points to /java/jdk7
  • ln -ns /java/jdk8 jdk update symlink jdk to point to /java/jdk8

Checking logs

  • tail -f logfile output appended data as file grows (f=follow)
  • less +F logfile open file, and output appended data as file grows

Text manipulation

  • head file display first 10 lines
  • head -20 file display first 20 lines
  • tail file display last 10 lines
  • tail -5 file display last 5 lines
  • head -20 file | tail -1 display 20th line
  • cut -f3 file display 3rd field for each line, tab as separator
  • cut -d',' -f3 file display 3rd field for each line, , as separator
  • cut -c3-6 file display characters from 3rd to 6th position for each line
  • cut -c7- file display characters from 7th to end of each line

Sed

  • sed s/unix/linux file replace first occurrence of "unix with "linux"
  • sed s/unix/linux/3 file replace 3rd occurrence
  • sed s/unix/linux/g file replace all occurrences
  • sed s/unix/linux/3g file replace all occurrences starting from 3rd one
  • sed -i '1 d' file delete header of file
  • sed -i '$ d' file delete footer of file
  • sed –n '10 p' file print 10th line of the file

Networking

  • ping hostname or telnet hostname port check if remote host is alive
  • scp /dir/file user@hostname:/targetdir/file copy file to different host
  • netstat -a | grep "port" check host connected to machine's port

Space

  • df -h space in current drive (-h is human readable format)
  • du -h . sizes of all files in current directory
  • du -sh . sizes of current directory
  • du /bin/* | sort -n sort all files based on size (asc)

Miscellaneous

  • lsof file list processes using the file
  • rev file reverses the text in each line
  • echo "string" | rev reverses the string
  • sort file sorts file lines alphabetically
  • sort -n file sorts file lines numerically
  • uniq file filter out adjacent duplicate lines and print
  • uniq -c file print with count at the begining of each line of output
  • uniq -d file print only duplicates