while read loop always false - bash - bash

probably quite easy question for you but has been a while I'm stuck with this issue.
Basically i want to perform some operation in every csv file in a folder and i put together this simple script:
#!/bin/bash
for file in *.csv ;
do
echo $file #check
OLDIFS=$IFS
IFS=","
while read var1
do
echo $var1
done < $file
IFS=$OLDIFS
done
The csv files follow all the same format, 1 line and 12 variables like:
name,1,2,3,4,5,6,7,8,9,11
It seems to me that the while conditions is always false and never run.
Could you tell me where I'm wrong?

To get just the first field, you need to supply two arguments to read; the first for the first field, the second to hold the remaining values after the split.
#!/bin/bash
for file in *.csv; do
echo $file #check
while IFS=, read name rest; do
echo "$name"
done < "$file"
done

Something like this should work. It reads the file into an array, splitting it at every ,. It the iterates over the array and prints out each element on a new line.
#!/bin/bash
for file in *.csv
do
echo "$file" #check
IFS=',' read -a vars < "$file"
for var1 in ${vars[#]}
do
echo "$var1"
done
done

Related

Reading file with read -r field1 field2 produce blank type [duplicate]

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

Looping for with cat and data with spaces [duplicate]

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

Reading files line by line in by using for loop bash script [duplicate]

This question already has answers here:
Looping through the content of a file in Bash
(16 answers)
Closed 3 years ago.
Say for example I have a file called "tests",it contains
a
b
c
d
I'm trying to read this file line by line and it should output
a
b
c
d
I create a bash script called "read" and try to read this file by using for loop
#!/bin/bash
for i in ${1}; do //for the ith line of the first argument, do...
echo $i // prints ith line
done
I execute it
./read tests
but it gives me
tests
Does anyone know what happened? Why does it print "tests" instead of the content of the "tests"? Thanks in advance.
#!/bin/bash
while IFS= read -r line; do
echo "$line"
done < "$1"
This solution can handle files with special characters in the file name (like spaces or carriage returns) unlike other responses.
You need something like this rather:
#!/bin/bash
while read line || [[ $line ]]; do
echo $line
done < ${1}
what you've written after expansion will become:
#!/bin/bash
for i in tests; do
echo $i
done
if you still want for loop, do something like:
#!/bin/bash
for i in $(cat ${1}); do
echo $i
done
This works for me:
#!/bin/sh
for i in `cat $1`
do
echo $i
done

Read a file line by line assigning the value to a variable [duplicate]

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

bash search for string in each line of file

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.

Resources