How to check if the list of numbers are sorted?

Question

How to check if numbers from list file are increasing?

Example list1:

658
659
663

will get "OK".

Example list2:

658
664
663

will get "FAIL".

Example list3:

23
24
25
26

will get "OK".

Answer 1

You can use sort -nc filename to validate if the file is in incremental order or not (containing numbers only).

sort -n -c filename >/dev/null 2>&1 && echo "OK" || echo "FAIL"

Or in short (note the upper -C "like -c, but do not report first bad line"), also using -u option to check for a strictly ascending order as well as -g option to have more number formats to be supported (like +2, 0x10, 1.2e+3, infinity, ... ) suggested by @StéphaneChazelas:

sort -guC filename && echo "OK" || echo "FAIL"

Note: if you don't want report "FAIL" on the repeated same numbers, omit the -u option at above.

Answer 2

awk 'BEGIN {res = "OK"}
     NR > 1 && $1 <= prev {res = "Fail"; exit}
     {prev = $1}
     END {print res}'  file

This awk solution should work. Set the res variable to OK from the outset and then check the first space delimited field in the file against the prev variable. If this line's $1 is less than the previous, set res to Fail and stop reading. Finally at the end of the script, print the res variable.

Answer 3

Another trick with join command:

join --check-order file file &>/dev/null && echo "OK" || echo "FAIL"

Tests:

$ cat a1
11
33
22
$ join --check-order a1 a1 &>/dev/null && echo "OK" || echo "FAIL"
FAIL

---

$ cat a2
11
22
33
$ join --check-order a2 a2 &>/dev/null && echo "OK" || echo "FAIL"
OK