seq

The seq command in Unix-like operating systems generates sequences of numbers, either in increasing or decreasing order. It's useful in shell scripting for iterating over a range of numbers or generating lists.

Basic Syntax

seq [options] [start] [increment] end

• options: Optional flags that modify the behavior of the seq command.

• start: The starting number of the sequence (default is 1).

• increment: The increment between numbers (default is 1).

• end: The ending number of the sequence.

Examples

Generating a Sequence of Numbers

# Generate numbers from 1 to 5
seq 1 5

Output:

1
2
3
4
5

Specifying Start and End

# Generate numbers from 5 to 10
seq 5 10

Output:

5
6
7
8
9
10

Generating Numbers with Increment

# Generate numbers from 1 to 10 with increment of 2
seq 1 2 10

Output:

1
3
5
7
9

Generating a Sequence in Reverse Order

# Generate numbers from 10 to 1
seq 10 -1 1

Output:

10
9
8
7
6
5
4
3
2
1

Practical Use Cases

Looping with for and seq

# Loop through numbers from 1 to 5
for i in $(seq 1 5)
do
  echo "Number: $i"
done

Creating Directories

# Create directories dir1 to dir5
for i in $(seq 1 5)
do
  mkdir "dir$i"
done

File Operations

# Create empty files file1.txt to file10.txt
for i in $(seq 1 10)
do
  touch "file$i.txt"
done

Advanced Examples

Using seq in a for Loop

# Print squares of numbers from 1 to 5
for i in $(seq 1 5)
do
  echo "Square of $i is $(($i * $i))"
done

Generating a Fixed-Length Sequence

# Generate a sequence of 10 numbers starting from 100
seq 100 109

Output:

100
101
102
103
104
105
106
107
108
109

Conclusion

The seq command is a handy tool in shell scripting for generating sequences of numbers efficiently. It simplifies tasks such as looping through ranges of numbers, creating directories or files in batches, and performing mathematical operations in scripts. By leveraging seq, you can make your shell scripts more dynamic and versatile.