seq
The seq command is a handy tool to generate a sequence of numbers in ascending or descending order. Both integer and floating-point numbers are supported. You can also customize the formatting for numbers and the separator between them.
Integer sequences
You need three numbers to generate an arithmetic progression — start, step and stop. When you pass only a single number as the stop value, the default start and step values are assumed to be 1.
# start=1, step=1 and stop=3
$ seq 3
1
2
3
Passing two numbers are considered as start and stop values (in that order).
# start=25434, step=1 and stop=25437
$ seq 25434 25437
25434
25435
25436
25437
# start=-5, step=1 and stop=-3
$ seq -5 -3
-5
-4
-3
When you want to specify all the three numbers, the order is start, step and stop.
# start=1000, step=5 and stop=1010
$ seq 1000 5 1010
1000
1005
1010
By using a negative step value, you can generate sequences in descending order.
# no output
$ seq 3 1
# need to explicitly use a negative step value
$ seq 3 -1 1
3
2
1
$ seq 5 -5 -10
5
0
-5
-10
Floating-point sequences
Since 1 is the default start and step values, you need to change at least one of them to get floating-point sequences.
$ seq 0.5 3
0.5
1.5
2.5
$ seq 0.25 0.33 1.12
0.25
0.58
0.91
E-scientific notation is also supported.
$ seq 1.2e2 1.22e2
120
121
122
$ seq 1.2e2 0.752 1.22e2
120.000
120.752
121.504
Customizing separator
You can use the -s option to change the separator between the numbers of a sequence. Multiple characters are allowed. Depending on your shell you can use ANSI-C quoting to use escapes like \t instead of a literal tab character. A newline is always added at the end of the output.
$ seq -s' ' 4
1 2 3 4
$ seq -s: -2 0.75 3
-2.00:-1.25:-0.50:0.25:1.00:1.75:2.50
$ seq -s' - ' 4
1 - 2 - 3 - 4
$ seq -s$'\n\n' 3
1
2
3
Leading zeros
By default, the output will not have leading zeros, even if they are part of the numbers passed to the command.
$ seq 008 010
8
9
10
The -w option will equalize the width of the output numbers using leading zeros. The largest width between the start and stop values will be used.
$ seq -w 8 10
08
09
10
$ seq -w 0002
0001
0002
printf style formatting
You can use the -f option for printf style floating-point number formatting. See bash manual: printf for more details on formatting options.
$ seq -f'%g' -s: 1 0.75 3
1:1.75:2.5
$ seq -f'%.4f' -s: 1 0.75 3
1.0000:1.7500:2.5000
$ seq -f'%.3e' 1.2e2 0.752 1.22e2
1.200e+02
1.208e+02
1.215e+02
Limitations
As per the manual:
On most systems,
seqcan produce whole-number output for values up to at least2^53. Larger integers are approximated. The details differ depending on your floating-point implementation.
# example with approximate values
$ seq 100000000000000000000 3333 100000000000000010000
100000000000000000000
100000000000000003336
100000000000000006664
100000000000000010000
However, when limited to non-negative whole numbers, an increment of less than
200, and no format-specifying option,seqcan print arbitrarily large numbers.
# no approximation for smaller step values
$ seq 100000000000000000000000000000 100000000000000000000000000005
100000000000000000000000000000
100000000000000000000000000001
100000000000000000000000000002
100000000000000000000000000003
100000000000000000000000000004
100000000000000000000000000005
Exercises
The exercises directory has all the files used in this section.
1) Generate numbers from 42 to 45 in ascending order.
##### add your solution here
42
43
44
45
2) Why does the command shown below produce no output?
# no output
$ seq 45 42
# expected output
##### add your solution here
45
44
43
42
3) Generate numbers from 25 to 10 in descending order, with a step value of 5.
##### add your solution here
25
20
15
10
4) Is the sequence shown below possible to generate with seq? If so, how?
##### add your solution here
01.5,02.5,03.5,04.5,05.5
5) Modify the command shown below to customize the output numbering format.
$ seq 30.14 3.36 40.72
30.14
33.50
36.86
40.22
##### add your solution here
3.014e+01
3.350e+01
3.686e+01
4.022e+01