Storing the first 4 characters of a filename into a variable - bash

This follwing code is part of a script I am writing. Now, for the purposes of this script, I am assuming there is only 1 file in ./src, so this loop should only execute once. Now, in the loop somewhere, I want to take the first 4 characters of $f (the filename) and store it in another variable. I know there is the cut command but I'm not sure if or how that would be used here because I thought cut was used for contents of files, not the files themselves.
for f in `ls ./src`
do
echo $f
cd tmp
f="../src/$f"
sh "$f"
done

From http://tldp.org/LDP/abs/html/string-manipulation.html
Substring Extraction
${string:position}
Extracts substring from $string at $position.
If the $string parameter is "*" or "#", then this extracts the positional parameters, [1] starting at $position.
${string:position:length}
Extracts $length characters of substring from $string at $position.
Example
shortName=${f:0:4}
Have fun!

You can use pure bash way:
${parameter:offset:length}
i.e. to get first chars of $HOME variable:
echo ${HOME:0:4}
btw your script is also faulty (never parse ls output). It should be like this:
for f in ./src/*
do
echo $f
cd tmp
f="../src/$f"
first4=${f:0:4}
sh "$f"
done

Related

Bash script MV is disappearing files

I've written a script to go through all the files in the directory the script is located in, identify if a file name contains a certain string and then modify the filename. When I run this script, the files that are supposed to be modified are disappearing. It appears my usage of the mv command is incorrect and the files are likely going to an unknown directory.
#!/bin/bash
string_contains="dummy_axial_y_position"
string_dontwant="dummy_axial_y_position_time"
file_extension=".csv"
for FILE in *
do
if [[ "$FILE" == *"$string_contains"* ]];then
if [[ "$FILE" != *"$string_dontwant"* ]];then
filename= echo $FILE | head -c 15
combined_name="$filename$file_extension"
echo $combined_name
mv $FILE $combined_name
echo $FILE
fi
fi
done
I've done my best to go through the possible errors I've made in the MV command but I haven't had any success so far.
There are a couple of problems and several places where your script can be improved.
filename= echo $FILE | head -c 15
This pipeline runs echo $FILE adding the variable filename having the null string as value in its environment. This value of the variable is visible only to the echo command, the variable is not set in the current shell. echo does not care about it anyway.
You probably want to capture the output of echo $FILE | head -c 15 into the variable filename but this is not the way to do it.
You need to use command substitution for this purpose:
filename=$(echo $FILE | head -c 15)
head -c outputs only the first 15 characters of the input file (they can be on multiple lines but this does not happen here). head is not the most appropriate way for this. Use cut -c-15 instead.
But for what you need (extract the first 15 characters of the value stored in the variable $FILE), there is a much simpler way; use a form of parameter expansion called "substring expansion":
filename=${FILE:0:15}
mv $FILE $combined_name
Before running mv, the variables $FILE and $combined_name are expanded (it is called "parameter expansion"). This means that the variable are replaced by their values.
For example, if the value of FILE is abc def and the value of combined_name is mnp opq, the line above becomes:
mv abc def mnp opq
The mv command receives 4 arguments and it attempts to move the files denoted by the first three arguments into the directory denoted by the fourth argument (and it probably fails).
In order to keep the values of the variables as single words (if they contain spaces), always enclose them in double quotes. The correct command is:
mv "$FILE" "$combined_name"
This way, in the example above, the command becomes:
mv "abc def" "mnp opq"
... and mv is invoked with two arguments: abc def and mnp opq.
combined_name="$filename$file_extension"
There isn't any problem in this line. The quotes are simply not needed.
The variables filename and file_extension are expanded (replaced by their values) but on assignments word splitting is not applied. The value resulted after the replacement is the value assigned to variable combined_name, even if it contains spaces or other word separator characters (spaces, tabs, newlines).
The quotes are also not needed here because the values do not contain spaces or other characters that are special in the command line. They must be quoted if they contain such characters.
string_contains="dummy_axial_y_position"
string_dontwant="dummy_axial_y_position_time"
file_extension=".csv"
It is not not incorrect to quote the values though.
for FILE in *
do
if [[ "$FILE" == *"$string_contains"* ]];then
if [[ "$FILE" != *"$string_dontwant"* ]]; then
This is also not wrong but it is inefficient.
You can use the expression from the if condition directly in the for statement (and get rid of the if statement):
for FILE in *"$string_contains"*; do
if [[ "$FILE" != *"$string_dontwant"* ]]; then
...
If you have read and understood the above (and some of the linked documentation) you will be able to figure out yourself where were your files moved :-)

Rename file to a hidden file for loop

I'm writing a fairly basic shell script that loops through files within a directory and renames the file and adds a dot(.) to the start of the file however it does not work
any insight on whats going wrong?
for file in /tmp/test/*; do
mv $file \\.$file;
done
There are two problems.
You're putting the dot before the whole pathname, not just the filename part.
You're prefixing the filename with \. instead of just .. There's no need for \\ in the mv command.
Corrected code:
for file in /tmp/test/*; do
mv "$file" "${file%/*}/.${file##*/}";
done
${file%/*} returns the value of $file with everything starting from the last / removed, which is the directory part of the pathname. ${file##*/}" returns the value of $file with everything up to the last / removed, which is the filename part. Then it puts them back together with /. between them, which adds the . prefix that you want to the filename part. See Bash parameter expansion documentation for details of these operators.
Also, remember to quote variables so you don't get errors when the variable contains whitespace.
This is a simple script that takes a directory argument:
hide_files.sh:
if [ $# -ne 1 ] || [ ! -d $1 ]; then
echo 'invalid dir arg.'
exit 1
fi
for f in $(ls $1); do
mv -v "$1/$f" "$1/.$f"
done
output:
$ bash hide_files.sh mydir
mydir/a -> mydir/.a
mydir/c -> mydir/.c

Remove suffix as well as prefix from path in bash

I have filepaths of the form:
../healthy_data/F35_HC_532d.dat
I want to extract F35_HC_532d from this. I can remove prefix and suffix from this filename in bash as:
for i in ../healthy_data/*; do echo ${i#../healthy_data/}; done # REMOVES PREFIX
for i in ../healthy_data/*; do echo ${i%.dat}; done # REMOVES SUFFIX
How can I combine these so that in a single command I would be able to remove both and extract only the part that I want?
You can use BASH regex for this like this and print captured group #1:
for file in ../healthy_data/*; do
[[ $file =~ .*/([_[:alnum:]]+)\.dat$ ]] && echo "${BASH_REMATCH[1]}"
done
If you can use Awk, it is pretty simple,
for i in ../healthy_data/*
do
stringNeeded=$(awk -F/ '{split($NF,temp,"."); print temp[1]}' <<<"$i")
printf "%s\n" "$stringNeeded"
done
The -F/ splits the input string on / character, and $NF represents the last field in the string in that case, F35_HC_532d.dat, now the split() function is called with the de-limiter . to extract the part before the dot.
The options/functions in the above Awk are POSIX compatible.
Also bash does not support nested parameter expansions, you need to modify in two fold steps something like below:-
tempString="${i#*/*/}"
echo "${tempString%.dat}"
In a single-loop,
for i in ../healthy_data/*; do tempString="${i#*/*/}"; echo "${tempString%.dat}" ; done
The two fold syntax here, "${i#*/*/}" part just stores the F35_HC_532d.dat into the variable tempString and in that variable we are removing the .dat part as "${tempString%.dat}"
If all files end with .dat (as you confirmed) you can use the basename command:
basename -s .dat /path/to/files/*
If there are many(!) of those files, use find to avoid an argument list too long error:
find /path/to/files -maxdepth 1 -name '*.dat' -exec basename -s .dat {} +
For a shell script which needs to deal if any number of .dat files use the second command!
Do you count this as one step?
for i in ../healthy_data/*; do
sed 's#\.[^.]*##'<<< "${i##*/}"
done
You can't strip both a prefix and suffix in a single parameter expansion.
However, this can be accomplished in a single loop using parameter expansion operations only. Just save the prefix stripped expansion to a variable and use expansion again to remove its suffix:
for file in ../healthy_data/*; do
prefix_stripped="${file##*\/healthy_data\/}"
echo "${prefix_stripped%.dat}"
done
If you are on zsh, one way to achieve this without the need for defining another variable is
for i in ../healthy_data/*; do echo "${${i#../healthy_data/}%.dat}"; done
This removes prefix and suffix in one step.
In your specific example the prefix stems from the fact that the files are located in a different directory. You can get rid of the prefix by cding in this case.
(cd ../healthy_data ; for i in *; do echo ${i%.dat}; done)
The (parens) invoke a sub shell process and your current shell stays where it is. If you don't want a sub shell you can cd back easily:
cd ../healthy_data ; for i in *; do echo ${i%.dat}; done; cd -

List all the files with prefixes from a for loop using Bash

Here is a small[but complete] part of my bash script that finds and outputs all files in mydir if the have the prefix from a stored array. Strange thing I notice is that this script works perfectly if I take out the "-maxdepth 1 -name" from the script else it only gives me the files with the prefix of the first element in the array.
It would be of great help if someone explained this to me. Sorry in advance if there is some thing obviously silly that I'm doing. I'm relatively new to scripting.
#!/bin/sh
DIS_ARRAY=(A B C D)
echo "Array is : "
echo ${DIS_ARRAY[*]}
for dis in $DIS_ARRAY
do
IN_FILES=`find /mydir -maxdepth 1 -name "$dis*.xml"`
for file in $IN_FILES
do
echo $file
done
done
Output:
/mydir/Abc.xml
/mydir/Ab.xml
/mydir/Ac.xml
Expected Output:
/mydir/Abc.xml
/mydir/Ab.xml
/mydir/Ac.xml
/mydir/Bc.xml
/mydir/Cb.xml
/mydir/Dc.xml
The loop is broken either way. The reason why
IN_FILES=`find mydir -maxdepth 1 -name "$dis*.xml"`
works, whereas
IN_FILES=`find mydir "$dis*.xml"`
doesn't is because in the first one, you have specified -name. In the second one, find is listing all the files in mydir. If you change the second one to
IN_FILES=`find mydir -name "$dis*.xml"`
you will see that the loop isn't working.
As mentioned in the comments, the syntax that you are currently using $DIS_ARRAY will only give you the first element of the array.
Try changing your loop to this:
for dis in "${DIS_ARRAY[#]}"
The double quotes around the expansion aren't strictly necessary in your specific case, but required if the elements in your array contained spaces, as demonstrated in the following test:
#!/bin/bash
arr=("a a" "b b")
echo using '$arr'
for i in $arr; do echo $i; done
echo using '${arr[#]}'
for i in ${arr[#]}; do echo $i; done
echo using '"${arr[#]}"'
for i in "${arr[#]}"; do echo $i; done
output:
using $arr
a
a
using ${arr[#]}
a
a
b
b
using "${arr[#]}"
a a
b b
See this related question for further details.
#TomFenech's answer solves your problem, but let me suggest other improvements:
#!/usr/bin/env bash
DIS_ARRAY=(A B C D)
echo "Array is : "
echo ${DIS_ARRAY[*]}
for dis in "${DIS_ARRAY[#]}"
do
for file in "/mydir/$dis"*.xml
do
if [ -f "$file" ]; then
echo "$file"
fi
done
done
Your shebang line references sh, but your question is tagged bash - unless you need POSIX compliance, use a bash shebang line to take advantage of all that bash has to offer
To match files located directly in a given directory (i.e., if you don't need to traverse an entire subtree), use a glob (filename pattern) and rely on pathname expansion as in my code above - no need for find and command substitution.
Note that the wildcard char. * is UNquoted to ensure pathname expansion.
Caveat: if no matching files are found, the glob is left untouched (assuming the nullglob shell option is OFF, which it is by default), so the loop is entered once, with an invalid filename (the unexpanded glob) - hence the [ -f "$file" ] conditional to ensure that an actual match was found (as an aside: using bashisms, you could use [[ -f $file ]] instead).

convert a file path into string

I'm having an error trying to find a way to replace a string in a directory path with another string
sed: Error tryning to read from {directory_path}: It's a directory
The shell script
#!/bin/sh
R2K_SOURCE="source/"
R2K_PROCESSED="processed/"
R2K_TEMP_DIR=""
echo " Procesando archivos desde $R2K_SOURCE "
for file in $(find $R2K_SOURCE )
do
if [ -d $file ]
then
R2K_TEMP_DIR=$( sed 's/"$R2K_SOURCE"/"$R2K_PROCESSED"/g' $file )
echo "directorio $R2K_TEMP_DIR"
else
# some code executes
:
fi
done
# find $R2K_PROCCESED -type f -size -200c -delete
i'm understanding that the rror it's in this line
R2K_TEMP_DIR=$( sed 's/"$R2K_SOURCE"/"$R2K_PROCESSED"/g' $file )
but i don't know how to tell sh that treats $file variable as string and not as a directory object.
If you want ot replace part of path name you can echo path name and take it to sed over pipe.
Also you must enable globbing by placing sed commands into double quotes instead of single and change separator for 's' command like that:
R2K_TEMP_DIR=$(echo "$file" | sed "s:$R2K_SOURCE:$R2K_PROCESSED:g")
Then you will be able to operate with slashes inside 's' command.
Update:
Even better is to remove useless echo and use "here is string" instead:
R2K_TEMP_DIR=$(sed "s:$R2K_SOURCE:$R2K_PROCESSED:g" <<< "$file")
First, don't use:
for item in $(find ...)
because you might overload the command line. Besides, the for loop cannot start until the process in $(...) finishes. Instead:
find ... | while read item
You also need to watch out for funky file names. The for loop will cough on all files with spaces in them. THe find | while will work as long as files only have a single space in their name and not double spaces. Better:
find ... -print0 | while read -d '' -r item
This will put nulls between file names, and read will break on those nulls. This way, files with spaces, tabs, new lines, or anything else that could cause problems can be read without problems.
Your sed line is:
R2K_TEMP_DIR=$( sed 's/"$R2K_SOURCE"/"$R2K_PROCESSED"/g' $file )
What this is attempting to do is edit your $file which is a directory. What you want to do is munge the directory name itself. Therefore, you have to echo the name into sed as a pipe:
R2K_TEMP_DIR=$(echo $file | sed 's/"$R2K_SOURCE"/"$R2K_PROCESSED"/g')
However, you might be better off using environment variable parameters to filter your environment variable.
Basically, you have a directory called source/ and all of the files you're looking for are under that directory. You simply want to change:
source/foo/bar
to
processed/foo/bar
You could do something like this ${file#source/}. The # says this is a left side filter and it will remove the least amount to match the glob expression after the #. Check the manpage for bash and look under Parameter Expansion.
This, you could do something like this:
#!/bin/sh
R2K_SOURCE="source/"
R2K_PROCESSED="processed/"
R2K_TEMP_DIR=""
echo " Procesando archivos desde $R2K_SOURCE "
find $R2K_SOURCE -print0 | while read -d '' -r file
do
if [ -d $file ]
then
R2K_TEMP_DIR="processed/${file#source/}"
echo "directorio $R2K_TEMP_DIR"
else
# some code executes
:
fi
done
R2K_TEMP_DIR="processed/${file#source/}" removes the source/ from the start of $file and you merely prepend processed/ in its place.
Even better, it's way more efficient. In your original script, the $(..) creates another shell process to run your echo in which then pipes out to another process to run sed. (Assuming you use loentar's solution). You no longer have any subprocesses running. The whole modification of your directory name is internal.
By the way, this should also work too:
R2K_TEMP_DIR="$R2K_PROCESSED/${file#$R2K_SOURCE}"
I just didn't test that.

Resources