Linux

Table of contents

Find
Search
Processes
File permissions
List files
Symlinks
Checking logs
Text manipulation
Sed
Networking
Space
Miscellaneous
For more information

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

For more information

Art of Command Line