Posts Tagged ‘bash’
git: How to revert a file to a specific commit
October 19, 2015 | 
Author git checkout COMMIT_HASH file/to/revert |
Will bring the file/to/revert file to the state in COMMIT_HASH commit.
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Pattern Matching Hyphen-Minus Sign in Bash
I was trying to use the sed command to perform some changes to a text and stepped into an interesting “problem”; pattern matching the minus-hyphen (-) symbol.
Assume we have the following text:
something SoMeThiNg some-thing soMe_thing
and we want to match all the different versions of the word with one expression (one by one).
My initial idea was to use this regular expression:
's/[a-zA-Z\-\_]*/matched/' |
Naturally, I tried to escape the – sign. As you can see from the output, this doesn’t work:
$ sed 's/[a-zA-Z\-\_]*/matched/' test matched matched matched-thing matched |
The minus sign is not matched, because of its special meaning (setting ranges). In order to make the expression work, you need to move the “-” either in the beginning or in the end of the expression:
$ sed 's/[a-zA-Z\_-]*/matched/' test matched matched matched matched $ sed 's/[-a-zA-Z\_]*/matched/' test matched matched matched matched |
and leave it un-escaped!
Selecting a random file/folder of a folder in Linux
I always had the following problem: “How to select which movie (from the ones in my collection) to watch“. In the past, I had used the random (pseudo-random to be precise) capabilities of C, Java, Erlang, and Javascript to select the movie.
Today I wrote a simple script that selects a random content (file or folder) within a folder:
#! /bin/sh if [ $# -gt 0 ]; then cd "$1"; fi ls -1 | awk 'BEGIN {srand()} {x[NR] = $0} END {print "Selected", x[1 + int(rand() * NR)]}' |
Save it in a file (lets say srandom, make it executable:
$ chmod +x srandom |
and execute it either with 0 or 1 arguments. Without an argument, the selection is done from the contents of the srandom‘s container, else the path given as an argument is used.
$ ./srandom.sh Selected lrandom.html $ ./srandom.sh /bin Selected gzexe |
Update
A much more elegant solution:
$ ls -1 | shuf -n1 |
Removing the SVN metadata files (.svn/) in Linux
If you ever want to remove a folder from SVN control (clean the folder by removing the .snv metadata folders) in Linux, you can simply run the following command:
rm -rf $(find path/to/the/CORRECT/folder -type d -name .svn) |
where:
rm -rfis remove recursive force. Recursive for deleting the directories and their contents recursively and force for no prompting (for example, for write protected files)$(..)is the command substitution, that takes the output of a command and uses it as input for anotherfind path/to/the/CORRECT/folder -type d -name .svnis searching (recursively) for folders (d for directory) with the name .svn1 in the directory pointed bypath/to/the/CORRECT/folder
Be careful to use the correct path, else you can remove the svn metada for the wrong folder! A good approach can be to execute the find command without the rm, check the output, and then proceed to the remove :-).
—
1case sensitive, use -iname for insensitive
Extracting citations from a BibTex file using Linux terminal
I had a big (around 40 entries) BibTex file with the references of some papers I studied and I wanted to extract the citations in the format used for citing in Latex (\cite{AuthorYear}). Just today I read some tutorials about awk, so I thought “Let’s use it!!”.
An example BibTex file:
@article{Kotselidis2010, author = {Kotselidis, Christos and Lujan, Mikel and Ansari, Mohammad and Malakasis, Konstantinos and Kahn, Behram and Kirkham, Chris and Watson, Ian}, doi = {10.1109/IPDPS.2010.5470460}, isbn = {978-1-4244-6442-5}, journal = {2010 IEEE International Symposium on Parallel \& Distributed Processing (IPDPS)}, pages = {1--12}, publisher = {Ieee}, title = {{Clustering JVMs with software transactional memory support}}, url = {http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=5470460}, year = {2010} } @phdthesis{Zhang2009c, author = {Zhang, Bo}, keywords = {cache-coherence,contention manager,distributed transactional memory}, title = {{On the Design of Contention Managers and Cache-Coherence Protocols for Distributed Transactional Memory}}, year = {2009} } |
Solution
awk 'BEGIN{FS="[{,]"} /@/ {print "\\cite{"$2"}"}' filename.bib |
\cite{Zhang2009c}
\cite{Kotselidis2010}
In order to save the output in a file named cites.txt:
awk 'BEGIN{FS="[{,]"} /@/ {print "\\cite{"$2"}"}' filename.bib > cites.txt |
Hint: Use “>>” if you want to append the output. Single > creates a new file (if not existing), or empties the existing one and then appends the content..
If you want to know my “implementation” process, continue reading 😉
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Really simple batch renaming in Linux
While working on the photos section of trigonakis.com, I wanted to batch rename some photos, so after the renaming their new name would be prefix_i, where i is a incremental value. The following (stupidly) simple bash script provides the desired functionality:
#!/bin/bash INDEX=1 for i in *.$1; do echo item $INDEX: "$i" renamed to $2_$INDEX.$1 mv "$i" $2_$INDEX.$1 let INDEX=INDEX+1 done |
Usage:
#make the script executable chmod +x scriptname.sh #move the folder containing the files to be renamed mv from_path/scriptname.sh to_path/ #run the script ./scriptname.sh FILE_EXTENSION NAME_PREFIX #example: ./rnm.sh JPG photo |