Command substitution not working inside for loop condition
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for (( a=1;a<=$(wc -l sedtest1);a++ ));do echo $a; done
Gives me an error:
-bash: ((: a<=21 sedtest1: syntax error in expression (error token is "sedtest1")
bash for loop-device
asked Jan 22 at 17:03
user323587user323587
132
add a comment |
for (( a=1;a<=$(wc -l sedtest1);a++ ));do echo $a; done
Gives me an error:
-bash: ((: a<=21 sedtest1: syntax error in expression (error token is "sedtest1")
bash for loop-device
asked Jan 22 at 17:03
user323587user323587
132
add a comment |
for (( a=1;a<=$(wc -l sedtest1);a++ ));do echo $a; done
Gives me an error:
-bash: ((: a<=21 sedtest1: syntax error in expression (error token is "sedtest1")
bash for loop-device
asked Jan 22 at 17:03
user323587user323587
132
for (( a=1;a<=$(wc -l sedtest1);a++ ));do echo $a; done
Gives me an error:
-bash: ((: a<=21 sedtest1: syntax error in expression (error token is "sedtest1")
bash for loop-device
bash for loop-device
asked Jan 22 at 17:03
user323587user323587
132
asked Jan 22 at 17:03
user323587user323587
132
asked Jan 22 at 17:03
user323587user323587
132
asked Jan 22 at 17:03
user323587user323587
132
asked Jan 22 at 17:03
user323587user323587
132
132
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
The output of wc -l sedtest1 will be something like:
21 sedtest1
So the test will become something like a <= 1234 sedtest1 which is invalid.
Also, that does mean that the wc command will be run for each iteration of the loop. If the content of the sedtest1 file doesn't change between each iteration, it would be better to save that number of line first in a variable outside the loop:
n=$(wc -l < sedtest1) # using redirection avoids the output containing the filename
for ((a = 0; a < n; a++)); do echo "$a"; done
I also suspect that you're trying to use a loop to process text in an inefficient and non-shell way. You may want to read Why is using a shell loop to process text considered bad practice?. Looping over each line of a file in that way is not the right way to go.
answered Jan 22 at 17:09
Stéphane ChazelasStéphane Chazelas
305k57574928
Thanks for the sources, I'll look into them!
– user323587
Jan 22 at 17:30
add a comment |
Nevermind I was just being incredibly stupid...wc -l file outputs as "x file".
All I had to do was this:for (( a=1;a<=$(wc -l sedtest1|awk 'print $1');a++ ));do echo $a; done
answered Jan 22 at 17:09
user323587user323587
132
1
Umm... Now you've made the code worse. Thewcandawkwill be invoked in each iteration of the loop. If the file is large, this would run very slowly. See Stéphane Chazelas' answer.
– Kusalananda
Jan 22 at 17:16
Oh I didn't say my answer was better, I just figured out the problem :D
– user323587
Jan 22 at 17:28
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
The output of wc -l sedtest1 will be something like:
21 sedtest1
So the test will become something like a <= 1234 sedtest1 which is invalid.
Also, that does mean that the wc command will be run for each iteration of the loop. If the content of the sedtest1 file doesn't change between each iteration, it would be better to save that number of line first in a variable outside the loop:
n=$(wc -l < sedtest1) # using redirection avoids the output containing the filename
for ((a = 0; a < n; a++)); do echo "$a"; done
I also suspect that you're trying to use a loop to process text in an inefficient and non-shell way. You may want to read Why is using a shell loop to process text considered bad practice?. Looping over each line of a file in that way is not the right way to go.
answered Jan 22 at 17:09
Stéphane ChazelasStéphane Chazelas
305k57574928
Thanks for the sources, I'll look into them!
– user323587
Jan 22 at 17:30
add a comment |
The output of wc -l sedtest1 will be something like:
21 sedtest1
So the test will become something like a <= 1234 sedtest1 which is invalid.
Also, that does mean that the wc command will be run for each iteration of the loop. If the content of the sedtest1 file doesn't change between each iteration, it would be better to save that number of line first in a variable outside the loop:
n=$(wc -l < sedtest1) # using redirection avoids the output containing the filename
for ((a = 0; a < n; a++)); do echo "$a"; done
I also suspect that you're trying to use a loop to process text in an inefficient and non-shell way. You may want to read Why is using a shell loop to process text considered bad practice?. Looping over each line of a file in that way is not the right way to go.
answered Jan 22 at 17:09
Stéphane ChazelasStéphane Chazelas
305k57574928
Thanks for the sources, I'll look into them!
– user323587
Jan 22 at 17:30
add a comment |
The output of wc -l sedtest1 will be something like:
21 sedtest1
So the test will become something like a <= 1234 sedtest1 which is invalid.
Also, that does mean that the wc command will be run for each iteration of the loop. If the content of the sedtest1 file doesn't change between each iteration, it would be better to save that number of line first in a variable outside the loop:
n=$(wc -l < sedtest1) # using redirection avoids the output containing the filename
for ((a = 0; a < n; a++)); do echo "$a"; done
I also suspect that you're trying to use a loop to process text in an inefficient and non-shell way. You may want to read Why is using a shell loop to process text considered bad practice?. Looping over each line of a file in that way is not the right way to go.
answered Jan 22 at 17:09
Stéphane ChazelasStéphane Chazelas
305k57574928
The output of wc -l sedtest1 will be something like:
21 sedtest1
So the test will become something like a <= 1234 sedtest1 which is invalid.
Also, that does mean that the wc command will be run for each iteration of the loop. If the content of the sedtest1 file doesn't change between each iteration, it would be better to save that number of line first in a variable outside the loop:
n=$(wc -l < sedtest1) # using redirection avoids the output containing the filename
for ((a = 0; a < n; a++)); do echo "$a"; done
I also suspect that you're trying to use a loop to process text in an inefficient and non-shell way. You may want to read Why is using a shell loop to process text considered bad practice?. Looping over each line of a file in that way is not the right way to go.
answered Jan 22 at 17:09
Stéphane ChazelasStéphane Chazelas
305k57574928
answered Jan 22 at 17:09
Stéphane ChazelasStéphane Chazelas
305k57574928
answered Jan 22 at 17:09
Stéphane ChazelasStéphane Chazelas
305k57574928
answered Jan 22 at 17:09
Stéphane ChazelasStéphane Chazelas
305k57574928
305k57574928
Thanks for the sources, I'll look into them!
– user323587
Jan 22 at 17:30
add a comment |
Thanks for the sources, I'll look into them!
– user323587
Jan 22 at 17:30
Thanks for the sources, I'll look into them!
– user323587
Jan 22 at 17:30
Thanks for the sources, I'll look into them!
– user323587
Jan 22 at 17:30
add a comment |
Nevermind I was just being incredibly stupid...wc -l file outputs as "x file".
All I had to do was this:for (( a=1;a<=$(wc -l sedtest1|awk 'print $1');a++ ));do echo $a; done
answered Jan 22 at 17:09
user323587user323587
132
1
Umm... Now you've made the code worse. Thewcandawkwill be invoked in each iteration of the loop. If the file is large, this would run very slowly. See Stéphane Chazelas' answer.
– Kusalananda
Jan 22 at 17:16
Oh I didn't say my answer was better, I just figured out the problem :D
– user323587
Jan 22 at 17:28
add a comment |
Nevermind I was just being incredibly stupid...wc -l file outputs as "x file".
All I had to do was this:for (( a=1;a<=$(wc -l sedtest1|awk 'print $1');a++ ));do echo $a; done
answered Jan 22 at 17:09
user323587user323587
132
1
Umm... Now you've made the code worse. Thewcandawkwill be invoked in each iteration of the loop. If the file is large, this would run very slowly. See Stéphane Chazelas' answer.
– Kusalananda
Jan 22 at 17:16
Oh I didn't say my answer was better, I just figured out the problem :D
– user323587
Jan 22 at 17:28
add a comment |
Nevermind I was just being incredibly stupid...wc -l file outputs as "x file".
All I had to do was this:for (( a=1;a<=$(wc -l sedtest1|awk 'print $1');a++ ));do echo $a; done
answered Jan 22 at 17:09
user323587user323587
132
Nevermind I was just being incredibly stupid...wc -l file outputs as "x file".
All I had to do was this:for (( a=1;a<=$(wc -l sedtest1|awk 'print $1');a++ ));do echo $a; done
answered Jan 22 at 17:09
user323587user323587
132
answered Jan 22 at 17:09
user323587user323587
132
answered Jan 22 at 17:09
user323587user323587
132
answered Jan 22 at 17:09
user323587user323587
132
132
1
Umm... Now you've made the code worse. Thewcandawkwill be invoked in each iteration of the loop. If the file is large, this would run very slowly. See Stéphane Chazelas' answer.
– Kusalananda
Jan 22 at 17:16
Oh I didn't say my answer was better, I just figured out the problem :D
– user323587
Jan 22 at 17:28
add a comment |
1
Umm... Now you've made the code worse. Thewcandawkwill be invoked in each iteration of the loop. If the file is large, this would run very slowly. See Stéphane Chazelas' answer.
– Kusalananda
Jan 22 at 17:16
Oh I didn't say my answer was better, I just figured out the problem :D
– user323587
Jan 22 at 17:28
1
1
Umm... Now you've made the code worse. The
wc and awk will be invoked in each iteration of the loop. If the file is large, this would run very slowly. See Stéphane Chazelas' answer.– Kusalananda
Jan 22 at 17:16
Umm... Now you've made the code worse. The
wc and awk will be invoked in each iteration of the loop. If the file is large, this would run very slowly. See Stéphane Chazelas' answer.– Kusalananda
Jan 22 at 17:16
Oh I didn't say my answer was better, I just figured out the problem :D
– user323587
Jan 22 at 17:28
Oh I didn't say my answer was better, I just figured out the problem :D
– user323587
Jan 22 at 17:28
add a comment |
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