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Use output of sed for a while read loop [duplicate]

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0

This question already has an answer here:

• 
  Loop through results of sed
  
  2 answers
  
  


• 
  Reading lines in a file and avoiding lines with # with Bash
  
  10 answers
  
  

I want the while loop to ignore blank (empty) lines and lines that contain #

I tried including sed -e 's/#.*$//' -e '/^$/d' on the input file and piping this into the while loop. This did not work.

file=$(sed -e 's/#.*$//' -e '/^$/d' foo.txt)

while IFS=: read -r f1 f2 f3 f4; do 

Command

done <"$file"

linux bash while-loop

share|improve this question

edited Mar 28 at 16:30

Charles Duffy

193k2929 gold badges222222 silver badges279279 bronze badges

asked Mar 28 at 16:05

KevinKevin

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marked as duplicate by tripleee bash
Users with the  bash badge can single-handedly close bash questions as duplicates and reopen them as needed.

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Mar 28 at 16:23

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

add a comment
 | 

0

This question already has an answer here:

• 
  Loop through results of sed
  
  2 answers
  
  


• 
  Reading lines in a file and avoiding lines with # with Bash
  
  10 answers
  
  

I want the while loop to ignore blank (empty) lines and lines that contain #

I tried including sed -e 's/#.*$//' -e '/^$/d' on the input file and piping this into the while loop. This did not work.

file=$(sed -e 's/#.*$//' -e '/^$/d' foo.txt)

while IFS=: read -r f1 f2 f3 f4; do 

Command

done <"$file"

linux bash while-loop

share|improve this question

edited Mar 28 at 16:30

Charles Duffy

193k2929 gold badges222222 silver badges279279 bronze badges

asked Mar 28 at 16:05

KevinKevin

1855 bronze badges

marked as duplicate by tripleee bash
Users with the  bash badge can single-handedly close bash questions as duplicates and reopen them as needed.

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Mar 28 at 16:23

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

add a comment
 | 

This question already has an answer here:

• 
  Loop through results of sed
  
  2 answers
  
  


• 
  Reading lines in a file and avoiding lines with # with Bash
  
  10 answers
  
  

I want the while loop to ignore blank (empty) lines and lines that contain #

I tried including sed -e 's/#.*$//' -e '/^$/d' on the input file and piping this into the while loop. This did not work.

file=$(sed -e 's/#.*$//' -e '/^$/d' foo.txt)

while IFS=: read -r f1 f2 f3 f4; do 

Command

done <"$file"

linux bash while-loop

share|improve this question

edited Mar 28 at 16:30

Charles Duffy

193k2929 gold badges222222 silver badges279279 bronze badges

asked Mar 28 at 16:05

KevinKevin

1855 bronze badges

file=$(sed -e 's/#.*$//' -e '/^$/d' foo.txt)

while IFS=: read -r f1 f2 f3 f4; do 

Command

done <"$file"

share|improve this question

edited Mar 28 at 16:30

Charles Duffy

193k2929 gold badges222222 silver badges279279 bronze badges

asked Mar 28 at 16:05

KevinKevin

1855 bronze badges

share|improve this question

edited Mar 28 at 16:30

Charles Duffy

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asked Mar 28 at 16:05

KevinKevin

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edited Mar 28 at 16:30

Charles Duffy

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edited Mar 28 at 16:30

Charles Duffy

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asked Mar 28 at 16:05

KevinKevin

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asked Mar 28 at 16:05

KevinKevin

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3 Answers
3

active

oldest

votes

4

You're trying to open that output as a filename, which it almost certainly isn't.

Run sed in a subshell and redirect its output to while loop instead.

while IFS=: read -r f1 f2 f3 f4; do
 # do something
done < <(sed -e 's/#.*$//' -e '/^$/d' foo.txt)

For anyone interested in how the syntax used in this answer works, see the bash-hackers' wiki on process substitution, and for why this syntax is better than sed ... | while read ..., see BashFAQ #24.

share|improve this answer

edited Mar 28 at 16:23

Charles Duffy

193k2929 gold badges222222 silver badges279279 bronze badges

answered Mar 28 at 16:07

oguz ismailoguz ismail

12.8k77 gold badges1919 silver badges3737 bronze badges

add a comment
 | 

0

You can use grep:

grep -Ev '^s*$|^s*#' foo.txt | while IFS=: read -r f1 f2 f3 f4; do 
 Command
done

share|improve this answer

answered Mar 28 at 16:18

accdiasaccdias

1,10799 silver badges1414 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Even grep -E isn't guaranteed to support s; only the regex syntax documented in the POSIX ERE standard is available across all platforms, and s -- like other backslash-sequence shorthand -- isn't there. To have guaranteed support on all POSIX platforms, use [[:space:]] instead.
  
  – Charles Duffy
  Mar 28 at 16:21
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ...so, the use of grep doesn't fix anything (the old sed command worked fine), and (with the use of s) introduces portability issues; the use of a pipe does fix the OP's problem, but it fixes it in a way that introduces different bugs.
  
  – Charles Duffy
  Mar 28 at 16:22
  
  

  
  
  
  

add a comment
 | 

-2

use grep -v:

-v, --invert-match select non-matching lines

share|improve this answer

answered Mar 28 at 16:10

DimasDimas

7877 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  That certainly works, but the problem isn't with the sed code, it's with how they're getting its result into the while read loop. Thus, this answer replaces one piece of working code with a different piece of working code, but doesn't actually fix the bug the OP is asking about.
  
  – Charles Duffy
  Mar 28 at 16:13
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If you read the title, then yes. But this is the first line of the post: "I want the while loop to ignore blank (empty) lines and lines that contain #" OP tried with sed, I'm suggesting to use grep instead.
  
  – Dimas
  Apr 4 at 17:08
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Here's the thing, though -- the thing the OP tried with sed works fine. You're suggesting that they change the part that already works, not the part that's broken. The bug isn't caused by file=$(sed -e 's/#.*$//' -e '/^$/d' foo.txt) doing something other than what the OP expects it to, so changing that line to file=$(grep -v '#|^$') or whatever doesn't fix it.
  
  – Charles Duffy
  Apr 4 at 17:12
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ...instead, the problem is caused by <"$file" iterating over a file named by the output of their sed command, or your grep command; switching which of those two interchangable commands is used is irrelevant to whether they hit that issue unless the other, later code is fixed.
  
  – Charles Duffy
  Apr 4 at 17:15
  
  

  
  
  
  

add a comment
 | 

4

You're trying to open that output as a filename, which it almost certainly isn't.

Run sed in a subshell and redirect its output to while loop instead.

while IFS=: read -r f1 f2 f3 f4; do
 # do something
done < <(sed -e 's/#.*$//' -e '/^$/d' foo.txt)

For anyone interested in how the syntax used in this answer works, see the bash-hackers' wiki on process substitution, and for why this syntax is better than sed ... | while read ..., see BashFAQ #24.

share|improve this answer

edited Mar 28 at 16:23

Charles Duffy

193k2929 gold badges222222 silver badges279279 bronze badges

answered Mar 28 at 16:07

oguz ismailoguz ismail

12.8k77 gold badges1919 silver badges3737 bronze badges

add a comment
 | 

4

You're trying to open that output as a filename, which it almost certainly isn't.

Run sed in a subshell and redirect its output to while loop instead.

while IFS=: read -r f1 f2 f3 f4; do
 # do something
done < <(sed -e 's/#.*$//' -e '/^$/d' foo.txt)

For anyone interested in how the syntax used in this answer works, see the bash-hackers' wiki on process substitution, and for why this syntax is better than sed ... | while read ..., see BashFAQ #24.

share|improve this answer

edited Mar 28 at 16:23

Charles Duffy

193k2929 gold badges222222 silver badges279279 bronze badges

answered Mar 28 at 16:07

oguz ismailoguz ismail

12.8k77 gold badges1919 silver badges3737 bronze badges

add a comment
 | 

You're trying to open that output as a filename, which it almost certainly isn't.

Run sed in a subshell and redirect its output to while loop instead.

while IFS=: read -r f1 f2 f3 f4; do
 # do something
done < <(sed -e 's/#.*$//' -e '/^$/d' foo.txt)

For anyone interested in how the syntax used in this answer works, see the bash-hackers' wiki on process substitution, and for why this syntax is better than sed ... | while read ..., see BashFAQ #24.

share|improve this answer

edited Mar 28 at 16:23

Charles Duffy

193k2929 gold badges222222 silver badges279279 bronze badges

answered Mar 28 at 16:07

oguz ismailoguz ismail

12.8k77 gold badges1919 silver badges3737 bronze badges

while IFS=: read -r f1 f2 f3 f4; do
 # do something
done < <(sed -e 's/#.*$//' -e '/^$/d' foo.txt)

share|improve this answer

edited Mar 28 at 16:23

Charles Duffy

193k2929 gold badges222222 silver badges279279 bronze badges

answered Mar 28 at 16:07

oguz ismailoguz ismail

12.8k77 gold badges1919 silver badges3737 bronze badges

edited Mar 28 at 16:23

Charles Duffy

193k2929 gold badges222222 silver badges279279 bronze badges

edited Mar 28 at 16:23

Charles Duffy

193k2929 gold badges222222 silver badges279279 bronze badges

answered Mar 28 at 16:07

oguz ismailoguz ismail

12.8k77 gold badges1919 silver badges3737 bronze badges

answered Mar 28 at 16:07

oguz ismailoguz ismail

12.8k77 gold badges1919 silver badges3737 bronze badges

0

You can use grep:

grep -Ev '^s*$|^s*#' foo.txt | while IFS=: read -r f1 f2 f3 f4; do 
 Command
done

share|improve this answer

answered Mar 28 at 16:18

accdiasaccdias

1,10799 silver badges1414 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Even grep -E isn't guaranteed to support s; only the regex syntax documented in the POSIX ERE standard is available across all platforms, and s -- like other backslash-sequence shorthand -- isn't there. To have guaranteed support on all POSIX platforms, use [[:space:]] instead.
  
  – Charles Duffy
  Mar 28 at 16:21
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ...so, the use of grep doesn't fix anything (the old sed command worked fine), and (with the use of s) introduces portability issues; the use of a pipe does fix the OP's problem, but it fixes it in a way that introduces different bugs.
  
  – Charles Duffy
  Mar 28 at 16:22
  
  

  
  
  
  

add a comment
 | 

0

You can use grep:

grep -Ev '^s*$|^s*#' foo.txt | while IFS=: read -r f1 f2 f3 f4; do 
 Command
done

share|improve this answer

answered Mar 28 at 16:18

accdiasaccdias

1,10799 silver badges1414 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Even grep -E isn't guaranteed to support s; only the regex syntax documented in the POSIX ERE standard is available across all platforms, and s -- like other backslash-sequence shorthand -- isn't there. To have guaranteed support on all POSIX platforms, use [[:space:]] instead.
  
  – Charles Duffy
  Mar 28 at 16:21
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ...so, the use of grep doesn't fix anything (the old sed command worked fine), and (with the use of s) introduces portability issues; the use of a pipe does fix the OP's problem, but it fixes it in a way that introduces different bugs.
  
  – Charles Duffy
  Mar 28 at 16:22
  
  

  
  
  
  

add a comment
 | 

You can use grep:

grep -Ev '^s*$|^s*#' foo.txt | while IFS=: read -r f1 f2 f3 f4; do 
 Command
done

share|improve this answer

answered Mar 28 at 16:18

accdiasaccdias

1,10799 silver badges1414 bronze badges

grep -Ev '^s*$|^s*#' foo.txt | while IFS=: read -r f1 f2 f3 f4; do 
 Command
done

share|improve this answer

answered Mar 28 at 16:18

accdiasaccdias

1,10799 silver badges1414 bronze badges

answered Mar 28 at 16:18

accdiasaccdias

1,10799 silver badges1414 bronze badges

answered Mar 28 at 16:18

accdiasaccdias

1,10799 silver badges1414 bronze badges

-2

use grep -v:

-v, --invert-match select non-matching lines

share|improve this answer

answered Mar 28 at 16:10

DimasDimas

7877 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  That certainly works, but the problem isn't with the sed code, it's with how they're getting its result into the while read loop. Thus, this answer replaces one piece of working code with a different piece of working code, but doesn't actually fix the bug the OP is asking about.
  
  – Charles Duffy
  Mar 28 at 16:13
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If you read the title, then yes. But this is the first line of the post: "I want the while loop to ignore blank (empty) lines and lines that contain #" OP tried with sed, I'm suggesting to use grep instead.
  
  – Dimas
  Apr 4 at 17:08
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Here's the thing, though -- the thing the OP tried with sed works fine. You're suggesting that they change the part that already works, not the part that's broken. The bug isn't caused by file=$(sed -e 's/#.*$//' -e '/^$/d' foo.txt) doing something other than what the OP expects it to, so changing that line to file=$(grep -v '#|^$') or whatever doesn't fix it.
  
  – Charles Duffy
  Apr 4 at 17:12
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ...instead, the problem is caused by <"$file" iterating over a file named by the output of their sed command, or your grep command; switching which of those two interchangable commands is used is irrelevant to whether they hit that issue unless the other, later code is fixed.
  
  – Charles Duffy
  Apr 4 at 17:15
  
  

  
  
  
  

add a comment
 | 

-2

use grep -v:

-v, --invert-match select non-matching lines

share|improve this answer

answered Mar 28 at 16:10

DimasDimas

7877 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  That certainly works, but the problem isn't with the sed code, it's with how they're getting its result into the while read loop. Thus, this answer replaces one piece of working code with a different piece of working code, but doesn't actually fix the bug the OP is asking about.
  
  – Charles Duffy
  Mar 28 at 16:13
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If you read the title, then yes. But this is the first line of the post: "I want the while loop to ignore blank (empty) lines and lines that contain #" OP tried with sed, I'm suggesting to use grep instead.
  
  – Dimas
  Apr 4 at 17:08
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Here's the thing, though -- the thing the OP tried with sed works fine. You're suggesting that they change the part that already works, not the part that's broken. The bug isn't caused by file=$(sed -e 's/#.*$//' -e '/^$/d' foo.txt) doing something other than what the OP expects it to, so changing that line to file=$(grep -v '#|^$') or whatever doesn't fix it.
  
  – Charles Duffy
  Apr 4 at 17:12
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ...instead, the problem is caused by <"$file" iterating over a file named by the output of their sed command, or your grep command; switching which of those two interchangable commands is used is irrelevant to whether they hit that issue unless the other, later code is fixed.
  
  – Charles Duffy
  Apr 4 at 17:15
  
  

  
  
  
  

add a comment
 | 

use grep -v:

-v, --invert-match select non-matching lines

share|improve this answer

answered Mar 28 at 16:10

DimasDimas

7877 bronze badges

-v, --invert-match select non-matching lines

share|improve this answer

answered Mar 28 at 16:10

DimasDimas

7877 bronze badges

answered Mar 28 at 16:10

DimasDimas

7877 bronze badges

answered Mar 28 at 16:10

DimasDimas

7877 bronze badges