I'm reading some file paths and names from a text file and trying to test if file exists. I'm not sure what I'm doing wrong but first echo returns filepath and file name whilst the echo inside the if statement doesn't. Any ideas?
#!/bin/bash
while read line; do
echo $line
if [ -f "$line" ]; then
echo "found: $line"
fi
done < /mbackup/temp/images.txt
The only change is adding the -r option to read. That option is documented as:
Backslash does not act as an escape character. The backslash is considered to be part of the line. In particular, a backslash-newline pair may not then be used as a line continuation.
This helps prevent special characters in file names from interfering with your script.
I test this with files containing special characters and it works as you expected.
#!/bin/bash
while read -r line; do
echo $line
if [ -f "$line" ]; then
echo "found: $line"
fi
done < /mbackup/temp/images.txt
Related
This question already has answers here:
Looping through the content of a file in Bash
(16 answers)
Closed 2 years ago.
I have the following .txt file:
Marco
Paolo
Antonio
I want to read it line-by-line, and for each line I want to assign a .txt line value to a variable. Supposing my variable is $name, the flow is:
Read first line from file
Assign $name = "Marco"
Do some tasks with $name
Read second line from file
Assign $name = "Paolo"
The following reads a file passed as an argument line by line:
while IFS= read -r line; do
echo "Text read from file: $line"
done < my_filename.txt
This is the standard form for reading lines from a file in a loop. Explanation:
IFS= (or IFS='') prevents leading/trailing whitespace from being trimmed.
-r prevents backslash escapes from being interpreted.
Or you can put it in a bash file helper script, example contents:
#!/bin/bash
while IFS= read -r line; do
echo "Text read from file: $line"
done < "$1"
If the above is saved to a script with filename readfile, it can be run as follows:
chmod +x readfile
./readfile filename.txt
If the file isn’t a standard POSIX text file (= not terminated by a newline character), the loop can be modified to handle trailing partial lines:
while IFS= read -r line || [[ -n "$line" ]]; do
echo "Text read from file: $line"
done < "$1"
Here, || [[ -n $line ]] prevents the last line from being ignored if it doesn't end with a \n (since read returns a non-zero exit code when it encounters EOF).
If the commands inside the loop also read from standard input, the file descriptor used by read can be chanced to something else (avoid the standard file descriptors), e.g.:
while IFS= read -r -u3 line; do
echo "Text read from file: $line"
done 3< "$1"
(Non-Bash shells might not know read -u3; use read <&3 instead.)
I encourage you to use the -r flag for read which stands for:
-r Do not treat a backslash character in any special way. Consider each
backslash to be part of the input line.
I am citing from man 1 read.
Another thing is to take a filename as an argument.
Here is updated code:
#!/usr/bin/bash
filename="$1"
while read -r line; do
name="$line"
echo "Name read from file - $name"
done < "$filename"
Using the following Bash template should allow you to read one value at a time from a file and process it.
while read name; do
# Do what you want to $name
done < filename
#! /bin/bash
cat filename | while read LINE; do
echo $LINE
done
Use:
filename=$1
IFS=$'\n'
for next in `cat $filename`; do
echo "$next read from $filename"
done
exit 0
If you have set IFS differently you will get odd results.
Many people have posted a solution that's over-optimized. I don't think it is incorrect, but I humbly think that a less optimized solution will be desirable to permit everyone to easily understand how is this working. Here is my proposal:
#!/bin/bash
#
# This program reads lines from a file.
#
end_of_file=0
while [[ $end_of_file == 0 ]]; do
read -r line
# the last exit status is the
# flag of the end of file
end_of_file=$?
echo $line
done < "$1"
If you need to process both the input file and user input (or anything else from stdin), then use the following solution:
#!/bin/bash
exec 3<"$1"
while IFS='' read -r -u 3 line || [[ -n "$line" ]]; do
read -p "> $line (Press Enter to continue)"
done
Based on the accepted answer and on the bash-hackers redirection tutorial.
Here, we open the file descriptor 3 for the file passed as the script argument and tell read to use this descriptor as input (-u 3). Thus, we leave the default input descriptor (0) attached to a terminal or another input source, able to read user input.
For proper error handling:
#!/bin/bash
set -Ee
trap "echo error" EXIT
test -e ${FILENAME} || exit
while read -r line
do
echo ${line}
done < ${FILENAME}
Use IFS (internal field separator) tool in bash, defines the character using to separate lines into tokens, by default includes <tab> /<space> /<newLine>
step 1: Load the file data and insert into list:
# declaring array list and index iterator
declare -a array=()
i=0
# reading file in row mode, insert each line into array
while IFS= read -r line; do
array[i]=$line
let "i++"
# reading from file path
done < "<yourFullFilePath>"
step 2: now iterate and print the output:
for line in "${array[#]}"
do
echo "$line"
done
echo specific index in array: Accessing to a variable in array:
echo "${array[0]}"
The following will just print out the content of the file:
cat $Path/FileName.txt
while read line;
do
echo $line
done
I am trying to escape spaces in a path name /Volumes/NO NAME. I need to access files present within this directory via a bash script. I have used sed and printf commands and neither seems to have worked. The code I have so far:
while read line
do
if [[ -d ${line} ]]; then
echo "${line} is a directory. Skipping this.";
elif [[ -f ${line} ]]; then
spacedOutLine=`echo ${line} | sed -e 's/ /\\ /g'`;
#spacedOutLine=$(printf %q "$line");
echo "line = ${line} and spacedOutLine = ${spacedOutLine}";
else
echo "Some other type of file. Unrecognized.";
fi
done < ${2}
Neither of this seems to have worked. For an input like: /Volumes/NO NAME/hello.txt, the output is:
/Volumes/NO: No such file or directory
NAME/hello.txt: No such file or directory
I am on a Mac and using bash via the terminal. I have also gone through a lot of other posts on SO about this which have not helped me.
Use double quotes while calling the ${line} variable.
"${line}"
This question already has answers here:
Looping through the content of a file in Bash
(16 answers)
Closed 2 years ago.
I have the following .txt file:
Marco
Paolo
Antonio
I want to read it line-by-line, and for each line I want to assign a .txt line value to a variable. Supposing my variable is $name, the flow is:
Read first line from file
Assign $name = "Marco"
Do some tasks with $name
Read second line from file
Assign $name = "Paolo"
The following reads a file passed as an argument line by line:
while IFS= read -r line; do
echo "Text read from file: $line"
done < my_filename.txt
This is the standard form for reading lines from a file in a loop. Explanation:
IFS= (or IFS='') prevents leading/trailing whitespace from being trimmed.
-r prevents backslash escapes from being interpreted.
Or you can put it in a bash file helper script, example contents:
#!/bin/bash
while IFS= read -r line; do
echo "Text read from file: $line"
done < "$1"
If the above is saved to a script with filename readfile, it can be run as follows:
chmod +x readfile
./readfile filename.txt
If the file isn’t a standard POSIX text file (= not terminated by a newline character), the loop can be modified to handle trailing partial lines:
while IFS= read -r line || [[ -n "$line" ]]; do
echo "Text read from file: $line"
done < "$1"
Here, || [[ -n $line ]] prevents the last line from being ignored if it doesn't end with a \n (since read returns a non-zero exit code when it encounters EOF).
If the commands inside the loop also read from standard input, the file descriptor used by read can be chanced to something else (avoid the standard file descriptors), e.g.:
while IFS= read -r -u3 line; do
echo "Text read from file: $line"
done 3< "$1"
(Non-Bash shells might not know read -u3; use read <&3 instead.)
I encourage you to use the -r flag for read which stands for:
-r Do not treat a backslash character in any special way. Consider each
backslash to be part of the input line.
I am citing from man 1 read.
Another thing is to take a filename as an argument.
Here is updated code:
#!/usr/bin/bash
filename="$1"
while read -r line; do
name="$line"
echo "Name read from file - $name"
done < "$filename"
Using the following Bash template should allow you to read one value at a time from a file and process it.
while read name; do
# Do what you want to $name
done < filename
#! /bin/bash
cat filename | while read LINE; do
echo $LINE
done
Use:
filename=$1
IFS=$'\n'
for next in `cat $filename`; do
echo "$next read from $filename"
done
exit 0
If you have set IFS differently you will get odd results.
Many people have posted a solution that's over-optimized. I don't think it is incorrect, but I humbly think that a less optimized solution will be desirable to permit everyone to easily understand how is this working. Here is my proposal:
#!/bin/bash
#
# This program reads lines from a file.
#
end_of_file=0
while [[ $end_of_file == 0 ]]; do
read -r line
# the last exit status is the
# flag of the end of file
end_of_file=$?
echo $line
done < "$1"
If you need to process both the input file and user input (or anything else from stdin), then use the following solution:
#!/bin/bash
exec 3<"$1"
while IFS='' read -r -u 3 line || [[ -n "$line" ]]; do
read -p "> $line (Press Enter to continue)"
done
Based on the accepted answer and on the bash-hackers redirection tutorial.
Here, we open the file descriptor 3 for the file passed as the script argument and tell read to use this descriptor as input (-u 3). Thus, we leave the default input descriptor (0) attached to a terminal or another input source, able to read user input.
For proper error handling:
#!/bin/bash
set -Ee
trap "echo error" EXIT
test -e ${FILENAME} || exit
while read -r line
do
echo ${line}
done < ${FILENAME}
Use IFS (internal field separator) tool in bash, defines the character using to separate lines into tokens, by default includes <tab> /<space> /<newLine>
step 1: Load the file data and insert into list:
# declaring array list and index iterator
declare -a array=()
i=0
# reading file in row mode, insert each line into array
while IFS= read -r line; do
array[i]=$line
let "i++"
# reading from file path
done < "<yourFullFilePath>"
step 2: now iterate and print the output:
for line in "${array[#]}"
do
echo "$line"
done
echo specific index in array: Accessing to a variable in array:
echo "${array[0]}"
The following will just print out the content of the file:
cat $Path/FileName.txt
while read line;
do
echo $line
done
I'm trying what seems like a very simple task: use bash to search a file for strings, and if they exist, output those to another file. It could be jetlag, but this should work:
#!/bin/bash
cnty=CNTRY
for line in $(cat wheatvrice.csv); do
if [[ $line = *$cnty* ]]
then
echo $line >> wr_imp.csv
fi
done
I also tried this for completeness:
#!/bin/bash
cnty=CNTRY
for line in $(cat wheatvrice.csv); do
case $line in
*"$cnty"*) echo $line >> wr_imp.csv;;
*) echo "no";;
esac
done
both output everything, regardless of whether the line contains CNTRY or not, and I'm copy/pasting from seemingly reliable sources, so apparently there's something simple about bash-ness that I'm missing?
Don't use bash, use grep.
grep -F "$cnty" wheatvrice.csv >> wr_imp.csv
While I would suggest to simply use grep too, the question is open, why you approach didn't work. Here a self referential modification of your second approach - with keyword 'bash' to match itself:
#!/bin/bash
cnty=bash
while read -r line
do
case $line in
*${cnty}*)
echo $line " yes" >> bashgrep.log
;;
*)
echo "no"
;;
esac
done < bashgrep.sh
The keypoint is while read -r line ... < FILE. Your command with cat involves String splitting, so every single word is processed in the loop, not every line.
The same problem in example 1.
My input file's contents are:
welcome
welcome1
welcome2
My script is:
for groupline in `cat file`
do
echo $groupline;
done
I got the following output:
welcome
welcome1
welcome2
Why doesn't it print the empty line?
you need to set IFS to newline \n
IFS=$"\n"
for groupline in $(cat file)
do
echo "$groupline";
done
Or put double quotes. See here for explanation
for groupline in "$(cat file)"
do
echo "$groupline";
done
without meddling with IFS, the "proper" way is to use while read loop
while read -r line
do
echo "$line"
done <"file"
Because you're doing it all wrong. You want while not for, and you want read, not cat:
while read groupline
do
echo "$groupline"
done < file
The solution ghostdog74 provided is helpful, but has a flaw.
IFS could not use double quotes (at least in Mac OS X), but can use single quotes like:
IFS=$'\n'
It's nice but not dash-compatible, maybe this is better:
IFS='
'
The blank line will be eaten in the following program:
IFS='
'
for line in $(cat file)
do
echo "$line"
done
But you can not add double quotes around $(cat file), it will treat the whole file as one single string.
for line in "$(cat file)"
If want blank line also be processed, using the following
while read line
do
echo "$line"
done < file
Using IFS=$"\n" and var=$(cat text.txt) removes all the "n" characters from the output echo $var