Common Shell Commands Cheatsheet

Beginning of the .sh files

#!/bin/sh
# Must be put at the beginning of the .sh file

Create directory
```
mkdir $dir_name
```
If the directory existed, commands in the following steps will be stopped and warning will be sent.
Create directory with parents directories
```
mkdir -p $dir_name
```
If the directory existed, command in the following steps will not be stopped.
Find a file (f) / directory (d) with specific keywords and copy it to a directory
```
find $search_dir -maxdepth $search_depth$ -type $f or d$ -name $keyword(*) -exec cp '{}' $target_dir \;
```
- If the keyword is not strictly refined, * could be added after the keyword.
- The last backslash \ could not be missed.

Variables

# A random example to assess the subdirectory called Deep_learning_task
mission_name=Deep_learning_task
cd "../$mission_name"

# variable evaluation
num_start=0
num_end=5
run_time=$(num_start+num_end)

No space in the variable mission_name
Modified strings have quotation mark “”
Variable evaluation is also possible

Condition syntax

if [ expression ]
then
Statement(s) to be executed if true
else
Statement(s) to be executed if not true
fi

Loop control

NUMS="1 2 3 4 5 6 7"
for NUM in $NUMS
# for ((NUM=1; NUM< 8; NUM++))
do
Q=`expr $NUM % 2`
if [ $Q -eq 0 ]
then
   echo "Number is an even number!!"
   continue
fi
echo "Found odd number"
done

Print
```
echo "I am an echo function"
```

Copy files

cp $current_file $future_dir

With parent directories
```
cp --parents $current_file $future_dir
```
copy directory
```
cp -r $current_file $future_dir
```

Replace keyword

sed -i "s/$search_keyword/$new_keyword/" $operated_file

Please don’t forget s and three /

Compress and decompress
```
tar [options] [archive-file] [file or directory to be archived]
```
Options:
- c : Creates archive
- x : Extracts the archive
- f : creates archive with given filename
- v : Displays verbose information

# decompress
tar xfv $target_tar_file
# compress
tar cfv $target_tar_file $to_compress_dir1 $to_compress_dir1  

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