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More Bash Examples

Add text to all files

#option 1
for filename in *.md; do
    echo "for loop test" >> "$filename";
 done

# option 2
echo "my text" | tee -a *.md
Named after the T-splitter in plumbing, tee "splits" to the standard output and the file to write to. The -a is for append, rather than overwrite. So the for loop and this command do the same thing, tee just prints out "my text" on top of appending the files.

For Loop

for i in {1..5}
do
   echo "Welcome $i times"
done

Make three files and search all with grep , then remove

touch testfile1; echo I am file 1 > testfile3
touch testfile2; echo I am file 2 > testfile2
touch testfile3; echo I am file 3 > testfile3
touch testfile4; echo I am file 4 > testfile4
# OR
for i in 1 2 3 4
do
  touch "testfile${i}"
  echo "I am file ${i}" > "testfile${i}"
done

grep file testfile1 testfile2 testfile3

rm -v testfile*
#OR
rm -v te?tf?l?*
# ? is a single character wildcard

Cat (concatonate)

#concatonate files
echo "This is file1." > file1.txt
echo "This is file2." > file2.txt
cat file1.txt file2.txt > combined.txt

#print to stdout
cat combined.txt
cat can both be used to concatenate files or print to standard out (stdout), which is where you see it more commonly used.

While loop

Simple CPU monitor that prints out the load average every 3 seconds continuously.

while true; do
clear
cat /proc/loadavg
sleep 3

&& vs ;

  • semicolon runs sequentially
  • && runs only if the previous on succeeds 
    asdlkfjaaasldkfqwkler ; pwd
# will run

alasdfjanmsdqwuer && pwd 
# will NOT run

Pretty Colors

Green 

echo -e "\033[32;1mHello"
Red 
echo -e "\033[31;1mHello"

Downloading

  • tar: only supports .tar files
    • historically from tape archive, the name somehow stuck
  • wget: World Wide Web get
    • primarily for downloading
  • curl: Client URL
    • supports more protocols than wget (SCP, SFTP, SMB)
    • often considered better for scripting due to its return codes and more output options.
    • can download and upload
  • dpkg: Debian packages
    • for .deb packages on Debian systems (Ubuntu, Linux Mint)
  • apt: advanced package tool
    • will install all dependencies, not just single package