bash.md

Executable

1. Create file ex. script or script.sh.

touch script

2. Add #!/bin/bash to the top.

#!/bin/bash

echo foo

3.Make the script executable.

chmod u+x script

4. Run script

./script

Command

1. Put the script in a ~/bin directory.

2. Add this into ~/.bashrc

• Make it a command

alias script='cd $(~/bin/script)'

• Make it a shortcut (CTRL + F)

bind -x '"\C-f":"cd $(~/bin/script)"'

Line breaks

If the statement is correct without continuation, you need to use \. Therefore, the following works without a backslash, as you can't end a command with a &&.

# Doesn't need line break
echo 1 &&
echo 2

# Needs line break
echo 1 \
&& echo 2

echo 1 2 3 \
4

Variables

Setting a command's output into a variable.

all="$(ls ./all | wc -l)" &&
echo "all: ${all}" &&
resampled="$(ls ./resampled | wc -l)" &&
echo "resampled: ${resampled}"

Logical

&& - AND || - OR

Redirection

> - Redirect standard output and overwrite.
>> - Redirect standard output and append.
< - Redirect input to another command. Ex. mail [email protected] < to_do.txt

Piping

| - Uses the output of one command as the input of another.

Command Substitution

$(PROGRAM_PATH) - Use program output as variable. Ex. echo "$(/bin/date) - Hi" >> logfile.log

grep

Only works for searching files or standard outputs.

grep <CRITERIA> <PATH> - Returns all the lines containing the search criteria.

File movement

# Navigate to D:
cd /mnt/d

# List all files WITH new line. Pasted in Excel gives one name per cell vertically.
ls -1 > ../pics.txt

# A && B  – Run B only if A succeeded
# One command from main folder
cd 1 && ls -1 > ../pics.txt && cd ../2 && ls -1 >> ../pics.txt && cd ..

# Wihtout .jpg extension.
cd 1 && ls -1 | tr -d ".jpg" > ../pics.txt && cd ../2 && ls -1 | tr -d ".jpg" >> ../pics.txt && cd ..

# Navigate to folder with files. List all files and replace new line with comma (,) and export one folder up into .csv file.
ls -1 | tr "\\n" "," > ../pics.csv

# Append (>>) files from other folder
ls -1 | tr "\\n" "," >> ../pics.csv

# List the different files from folder 1 vs folder 2
diff <(ls -1a folder1) <(ls -1a folder2)

# Check for different files not present in folder2 from folder1, and MOVE those in folder3
rsync -rcC --compare-dest=folder2/ folder1/ folder3/

# Find all the files with a space in the name
find ./ -name "* *"

# Find all the files with a space in the name AND move them
find ./ -name "* *" -exec mv -t ../folder {} +

# Find all the files with a dash - in the name AND move them
find ./ -name "*-*" -exec mv -t ../temp {} +

# Find all files with 4 characters
find ./ -name "????.jpg"

# Find all files with 4 characters AND move them
find ./ -name "????.jpg" -exec mv -t ../folder {} +

# Count number of files in folder
ls | wc -l

# Count number of files in folder with 6 characters.
find ./ -name "??????.jpg" | wc -l

# List just the names of the images (without the extension).
ls -1 | sed -e 's/\..*$//' > ../pics.txt

Image manipulation

Requires the imagemagick package

sudo apt-get install imagemagick

Resizing

# Resize image to specific dimensions, while trying to keep aspect ratio.
convert image.jpg -resize 492x492 resized_image.jpg

# Bulk resizing of images in a folder with conversion statuses, saved in a specified folder.
for file in *.jpg; do convert $file -resize 492x492 ../resized/$file && echo $file converted; done

Resampling

sudo apt install imagemagick

# Reduce the image quality. Adjust the quality parameter 1-100.
convert image.jpg -sampling-factor 4:2:0 -strip -quality 1 -interlace JPEG -colorspace RGB resampled_image.jpg

# Bulk resampling of images in a folder with conversion statuses, saved in a specified folder.
for file in *.jpg; do convert $file -sampling-factor 4:2:0 -strip -quality 1 -interlace JPEG -colorspace RGB ../resampled/$file && echo $file resampled; done

Watermarking

# Watermarking
composite -dissolve 30% -gravity center watermark2.jpg image.jpg watermarked_image.jpg

# Bulk Watermarking (Save in a specific folder)
for file in *.jpg; do composite -dissolve 30% -gravity center ../watermark.jpg $file ./watered/$file && echo $file watermarked; done