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Seq command

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Seq is a little known Linux command which is actually quite useful in while loops as it  can generate integer and floating point sequences with given increment. With -f parameter it can also insert them into arbitrary text strings.

By default seq sends to standard output a sequence of numbers.

seq [OPTION]... LAST
seq [OPTION]... FIRST LAST
seq [OPTION]... FIRST INCREMENT LAST  

Options

-f, --format=FORMAT
use printf style floating-point FORMAT (default: %g)
-s, --separator=STRING
use STRING to separate numbers (default: \n)
-w, --equal-width
equalize width by padding with leading zeroes
--help
display this help and exit
--version
output version information and exit

If FIRST or INCREMENT is omitted, it defaults to 1. That is, an omitted INCREMENT defaults to 1 even when LAST is smaller than FIRST. FIRST, INCREMENT, and LAST are interpreted as floating point values. INCREMENT is usually positive if FIRST is smaller than LAST, and INCREMENT is usually negative if FIRST is greater than LAST. When given, the FORMAT argument must contain exactly one of the printf-style, floating point output formats %e, %f, %g  


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[Apr 26, 2018] Bash Range How to iterate over sequences generated on the shell Linux Hint by Fahmida Yesmin

Notable quotes:
"... When only upper limit is used then the number will start from 1 and increment by one in each step. ..."
Apr 26, 2018 | linuxhint.com

Bash Range: How to iterate over sequences generated on the shell 2 days ago You can iterate the sequence of numbers in bash by two ways. One is by using seq command and another is by specifying range in for loop. In seq command, the sequence starts from one, the number increments by one in each step and print each number in each line up to the upper limit by default. If the number starts from upper limit then it decrements by one in each step. Normally, all numbers are interpreted as floating point but if the sequence starts from integer then the list of decimal integers will print. If seq command can execute successfully then it returns 0, otherwise it returns any non-zero number. You can also iterate the sequence of numbers using for loop with range. Both seq command and for loop with range are shown in this tutorial by using examples.

The options of seq command:

You can use seq command by using the following options.

Examples of seq command:

You can apply seq command by three ways. You can use only upper limit or upper and lower limit or upper and lower limit with increment or decrement value of each step . Different uses of the seq command with options are shown in the following examples.

Example-1: seq command without option

When only upper limit is used then the number will start from 1 and increment by one in each step. The following command will print the number from 1 to 4.

$ seq 4

When the two values are used with seq command then first value will be used as starting number and second value will be used as ending number. The following command will print the number from 7 to 15.

$ seq 7 15

When you will use three values with seq command then the second value will be used as increment or decrement value for each step. For the following command, the starting number is 10, ending number is 1 and each step will be counted by decrementing 2.

$ seq 10 -2 1
Example-2: seq with –w option

The following command will print the output by adding leading zero for the number from 1 to 9.

$ seq -w 0110
Example-3: seq with –s option

The following command uses "-" as separator for each sequence number. The sequence of numbers will print by adding "-" as separator.

$ seq -s - 8

Example-4: seq with -f option

The following command will print 10 date values starting from 1. Here, "%g" option is used to add sequence number with other string value.

$ seq -f "%g/04/2018" 10

The following command is used to generate the sequence of floating point number using "%f" . Here, the number will start from 3 and increment by 0.8 in each step and the last number will be less than or equal to 6.

$ seq -f "%f" 3 0.8 6

Example-5: Write the sequence in a file

If you want to save the sequence of number into a file without printing in the console then you can use the following commands. The first command will print the numbers to a file named " seq.txt ". The number will generate from 5 to 20 and increment by 10 in each step. The second command is used to view the content of " seq.txt" file.

seq 5 10 20 | cat > seq.txt
cat seq.txt

Example-6: Using seq in for loop

Suppose, you want to create files named fn1 to fn10 using for loop with seq. Create a file named "sq1.bash" and add the following code. For loop will iterate for 10 times using seq command and create 10 files in the sequence fn1, fn2,fn3 ..fn10.

#!/bin/bash
for i in ` seq 10 ` ; do touch fn. $i done

Run the following commands to execute the code of the bash file and check the files are created or not.

bash sq1.bash
ls

Examples of for loop with range: Example-7: For loop with range

The alternative of seq command is range. You can use range in for loop to generate sequence of numbers like seq. Write the following code in a bash file named " sq2.bash ". The loop will iterate for 5 times and print the square root of each number in each step.

#!/bin/bash
for n in { 1 .. 5 } ; do (( result =n * n ))
echo $n square = $result
done

Run the command to execute the script of the file.

bash sq2.bash

Example-8: For loop with range and increment value

By default, the number is increment by one in each step in range like seq. You can also change the increment value in range. Write the following code in a bash file named " sq3.bash ". The for loop in the script will iterate for 5 times, each step is incremented by 2 and print all odd numbers between 1 to 10.

#!/bin/bash
echo "all odd numbers from 1 to 10 are"
for i in { 1 .. 10 .. 2 }; do echo $i ; done

Run the command to execute the script of the file.

bash sq3.bash

If you want to work with the sequence of numbers then you can use any of the options that are shown in this tutorial. After completing this tutorial, you will be able to use seq command and for loop with range more efficiently in your bash script.

[Dec 30, 2010] Seq command - revisited

September 12, 2006 | Wee Keat's Jumblog

I realised that I left out another crucial option for the seq command, that is the -f command. This is basically the formatting option, which allows you to format the results using the printf style floating-point FORMAT.

An example:

me@mycomp:~$
me@mycomp:~$ seq -f "line: %g" 1 5
line: 1
line: 2
line: 3
line: 4
line: 5

Now, with the option above, the practical side of it is now very obvious. Let's say I want to generate a pool of test email address… ahh… you see it too eh!

Here we go:

me@mycomp:~$
me@mycomp:~$ seq -f "email_%g@example.com" 1 5
email_1@example.com
email_2@example.com
email_3@example.com
email_4@example.com
email_5@example.com

Now, let's generate this email list and have them separated by comma.

me@mycomp:~$
me@mycomp:~$ seq -s ',' -f "email_%g@example.com" 1 5
me@mycomp:~$ mail_1@example.com,email_2@example.com,email_3@example.com,email_4@example.com,email_5@example.com

So… there you go, as promised, a nice and practical example of using the seq command. From now on, if you need a million sample emails in CSV format, just use the following:

me@mycomp:~$
me@mycomp:~$ seq -f "email_%g@example.com,firstname,lastname" 1 1000000 > emaillist.txt

You can also pipe them to other commands. Get creative!

Do you know about the obscure Linux command 'seq'????? It is actually quite cool.

Examples

seq 10
1
2
3
4
5
6
7
8
9
10
seq 3 9
3
4
5
6
7
8
9
seq 10 10 110
10
20
30
40
50
60
70
80
90
100
110

seq has c-style format capabilities. For example

seq -f "harvey%02g" 10

will produce a sequence of ten strings each starting with harvey and ending with a number:

harvey01
harvey02
harvey03
harvey04
harvey05
harvey06
harvey07
harvey08
harvey09
harvey10

To make these words into empty files, you use the "touch" comand. "touch" followed by a legal filename will update the timestamp of the file referred to. But, if there is no file of that name, touch creates it!

This can be used for generation of files like in the folllowing example:

touch $(seq -f "harvey%02g" 10)

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Last modified: September 02, 2019