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General command line tips

📂 Create a compressed archive and remove archived files in one command line:

tar --remove-files -czf archive.tar.gz *.ext

 

🔄 Display the result of a command and update/refresh it every PERIOD seconds:

PERIOD=2;         # update period (in seconds)
while [ 1 ];      # infinite loop
  do tput clear;  # clear the content of the terminal
  date;           # any quick command displaying information
  sleep $PERIOD;  # wait for PERIOD seconds
done

Works well as a one-liner too:

while [ 1 ]; do tput clear; date; sleep 2; done

 

🔗 Display the absolute path to an executable command cmd:

readlink -f $(which $cmd)

Example:

which mvn
# /usr/bin/mvn
readlink -f $(which mvn)
# /usr/local/apache-maven-3.2.5/bin/mvn

 

🔍 List all files containing some text:

find . -type f -exec grep -H <some_text> {} \; 2>/dev/null | cut -d':' -f1 | sort -u

Explanation:

# Find all files recursively in current directory.
find . -type f \
# For each file, search for <some_text> and format
# results this way: <file_name>:<matched_line>
-exec grep -H <some_text> {} \; \
# Ignore permission issues.
2>/dev/null \
# Filter on file names.
| cut -d':' -f1 \
# Remove duplicates (and sort).
| sort -u

 

📑 Find some expression in a file and display surrounding lines:

grep -B 2 -A 5 $some_expression $file
# display lines where the expression was found
# surrounded with 2 previous lines (B = before)
# and 5 following lines (A = after)

 

📊 Group and count text occurrences:

# Create a list of occurrences

for x in a b a c b b b a c a c a a b a; do
  echo $x | sed -e 's/a/Apple/' -e 's/b/Banana/' -e 's/c/Cherry/'
done > list

head -5 list
# Apple
# Banana
# Apple
# Cherry
# Banana

wc -l list
# 15
# Group and count occurrences

cat list | sort | uniq -c
#      7 Apple
#      5 Banana
#      3 Cherry

 

🔢 Compute basic metrics on a list of integers:

# Let's consider a file named 'unsorted-integers'
# containing unsorted integers (one integer per line).

sort -n unsorted-integers > sorted-integers; INPUT="sorted-integers"

echo "Min="$(head -1 $INPUT); \
echo "Max="$(tail -1 $INPUT); \
awk '{sum += $1} END {print "Count="NR; print"Total="sum; print "Average="sum/NR}' $INPUT

# Min=2861
# Max=110403
# Count=206
# Total=53591
# Average=15609

 

👪 Find everything owned by a user or a group:

sudo find / -user $USER
sudo find / -group $GROUP

 

💀 Delete a user or a group:

sudo userdel $USER
sudo groupdel $GROUP

 

➗ Fun code to delete one file out of two (unsafe for file names with spaces):

for f in *.xml; do [ -f rm ] && rm -f $f && rm rm || touch rm; done; rm -f rm;

 

👻 Prevent commands in a bash terminal from being stored in history:

  • HISTCONTROL environment variable should be set to ignorespace or ignoreboth (done by default on most systems)
  • type your command with a leading space to prevent storing it in history

 

🔐 Encrypt and decrypt a file by passphrase using GNU Privacy Guard:

gpg --output data-file.encrypted --symmetric --cipher-algo AES256 data-file
gpg --output data-file.decrypted --decrypt data-file.encrypted
# cksum on data-file.decrypted should give same result as on data-file

 

⏰ Display and schedule jobs using crontab:

# Display scheduled jobs for the current user:
crontab -l

# Display scheduled jobs for the specified user:
crontab -u ${some_user} -l

# Display scheduled jobs if crontab is not allowed:
(sudo) cat /var/spool/cron/crontabs/${some_user}

# Edit scheduled jobs for the current user:
crontab -e
# Run a script every working day, every hour, from 8 AM to 8 PM
0 8-20 * * 1-5 bash -c "/opt/some-script.sh"

# Start some service every day at 8 AM, stop it at 11 PM
0    8 * * * bash -c "/opt/some-service.sh start"
0   23 * * * bash -c "/opt/some-service.sh stop"