Introduction
At times you’ll want to determine the order in which code is executed by naming the source code files correspondingly. This “trick” is particularly popular in server software and operating systems development.
Here’s a “random example” of file sequencing (found on a Debian system):
1 /etc/rc2.d# ls -la | head 2 total 12 3 drwxr-xr-x 2 root root 4096 May 14 16:59 ./ 4 drwxr-xr-x 152 root root 8192 May 15 05:51 ../ 5 lrwxrwxrwx 1 root root 18 Mar 9 2003 S10sysklogd -> ../init.d/sysklogd* 6 lrwxrwxrwx 1 root root 15 Mar 9 2003 S11klogd -> ../init.d/klogd* 7 lrwxrwxrwx 1 root root 13 Apr 13 22:38 S14ppp -> ../init.d/ppp* 8 lrwxrwxrwx 1 root root 17 Apr 25 15:31 S15dnsmasq -> ../init.d/dnsmasq* 9 lrwxrwxrwx 1 root root 14 Mar 29 2003 S20alsa -> ../init.d/alsa* 10 lrwxrwxrwx 1 root root 16 Apr 30 11:13 S20cupsys -> ../init.d/cupsys* 11 lrwxrwxrwx 1 root root 18 Mar 12 16:45 S20darkstat -> ../init.d/darkstat*
The resequence.py tool (syntax highlighted code here) helps you to maintain such collections of files.
By the way, if you are writing Python code that needs to find and manipulate files you may also want to check out the scriptutil.py module described in this article.
Usage examples
Using the shell commands below I am creating 3 randomly named files in the files sub-directory (lines 3-5).
1 bbox33:resequence $ for n in `jot -r -c 15 a z | rs -g 0 5`; do touch files/$n; done 2 bbox33:resequence $ find . -type f | grep -v swp 3 ./files/emnuw 4 ./files/nnrln 5 ./files/qkmbe 6 ./resequence.py
The resequence.py tool invoked without any command line arguments will merely print a help text which is considered a security feature 🙂
7 bbox33:resequence $ python resequence.py 8 resequence.py: a tool to rename a set of numbered files so that they 9 are 10 "slots" apart. 10 11 resequence.py [-n] [-p path] [-v] 12 13 -c cmd | --cmd cmd : rename command to use (default: 'mv') 14 -n | --noaction : no action, just show what would be done 15 -p path | --path path : path where the files reside 16 -v | --verbose : verbose output 17 18 For help use --help
When invoked with the -n (“no action”) command line argument, the tool will only print a summary of what needs to be done but will not take any action.
19 bbox33:resequence $ python resequence.py -n -p files 20 mv files/emnuw files/010-emnuw 21 mv files/nnrln files/020-nnrln 22 mv files/qkmbe files/030-qkmbe
When run with the -v command line argument, the tool will actually rename files as needed and show what is being done (since it is invoked in “verbose” mode).
23 bbox33:resequence $ python resequence.py -v -p files 24 running: 'mv files/emnuw files/010-emnuw' 25 running: 'mv files/nnrln files/020-nnrln' 26 running: 'mv files/qkmbe files/030-qkmbe'
Here I am adding one more file (see lines 27 and 32)..
27 bbox33:resequence $ touch files/another 28 bbox33:resequence $ find . -type f | grep -v swp 29 ./files/010-emnuw 30 ./files/020-nnrln 31 ./files/030-qkmbe 32 ./files/another 33 ./resequence.py
.. and calling the tool to show me what needs to be done (line 34) and to actually do the job (line 36).
34 bbox33:resequence $ python resequence.py -n -p files 35 mv files/another files/040-another 36 bbox33:resequence $ python resequence.py -v -p files 37 ok: files/010-emnuw 38 ok: files/020-nnrln 39 ok: files/030-qkmbe 40 running: 'mv files/another files/040-another'
In the example below I am creating another file (see lines 41 and 46) that’s inserted in the existing sequence ..
41 bbox33:resequence $ touch files/035-xxx 42 bbox33:resequence $ find . -type f | grep -v swp 43 ./files/010-emnuw 44 ./files/020-nnrln 45 ./files/030-qkmbe 46 ./files/035-xxx 47 ./files/040-another 48 ./resequence.py
.. and, again, running the tool to rename the files as needed (line 52).
49 bbox33:resequence $ python resequence.py -n -p files 50 mv files/035-xxx files/040-xxx 51 mv files/040-another files/050-another 52 bbox33:resequence $ python resequence.py -v -p files 53 ok: files/010-emnuw 54 ok: files/020-nnrln 55 ok: files/030-qkmbe 56 running: 'mv files/035-xxx files/040-xxx' 57 running: 'mv files/040-another files/050-another'
Enjoy!
