I have a simple script: #!/bin/bash # index=0 total=0 names=() ip=() while read -r LINE do NODENAME=` echo $LINE | cut -f 1 -d ','` IP=` echo $LINE | cut -f 2 -d ','` names[index]="$NODENAME" ip[index]="$IP" index=`expr index+1` total=`expr total+1` done <<< $(cat list.txt)
simple file: more list.txt name1,ip1 name2,ip2 name3,ip3
output when running: sh -x ./test_bash.sh + index=0 + total=0 + names=() + ip=() ++ cat list.txt + read -r LINE ++ echo name1,ip1 name2,ip2 name3,ip3 ++ cut -f 1 -d , + NODENAME=name1 ++ echo name1,ip1 name2,ip2 name3,ip3 ++ cut -f 2 -d , + IP='ip1 name2' + names[index]=name1 + ip[index]='ip1 name2' ++ expr index+1 + index=index+1 ++ expr total+1 + total=total+1 + read -r LINE + echo name1 name1
Question is why is it not reading one line at a time ? All I get is the first one. I'm just trying to build the array of the items in the file and then list them at this point.
Thanks
Jerry
On 23/07/2020 15:46, Jerry Geis wrote:
Hi Jerry,
See below, inline, for some comments.
I have a simple script: #!/bin/bash # index=0 total=0 names=() ip=() while read -r LINE do NODENAME=` echo $LINE | cut -f 1 -d ','`
NODENAME=$(cut -d, -f1 <<< $LINE)
Notes: use $( instead of backticks. There's no need to quote the comma. Write less and write concisely.
IP=` echo $LINE | cut -f 2 -d ','`
IP=$(cut -d, -f2 <<< $LINE)
names[index]="$NODENAME" ip[index]="$IP"
ip[$((index++))]="$IP"
This allows you to use the variable index, and then increment it by one for the next cycle of the loop.
index=`expr index+1`
Not needed because of the post-increment (++) above.
total=`expr total+1`
((total++))
done <<< $(cat list.txt)
done < list.txt
The "<<<" operator does all manner of expansion of the input and supplies it as a single line. That not what you want. Just redirect stdin from the file instead.
simple file: more list.txt name1,ip1 name2,ip2 name3,ip3
output when running: sh -x ./test_bash.sh
- index=0
- total=0
- names=()
- ip=()
++ cat list.txt
- read -r LINE
++ echo name1,ip1 name2,ip2 name3,ip3
This is happening because of the <<< operator.
++ cut -f 1 -d ,
- NODENAME=name1
++ echo name1,ip1 name2,ip2 name3,ip3 ++ cut -f 2 -d ,
- IP='ip1 name2'
- names[index]=name1
- ip[index]='ip1 name2'
++ expr index+1
- index=index+1
++ expr total+1
- total=total+1
- read -r LINE
- echo name1
name1
Question is why is it not reading one line at a time ? All I get is the first one. I'm just trying to build the array of the items in the file and then list them at this point.
Thanks, when I change it do the following I get a syntax error
#!/bin/bash # while read LINE do echo $LINE done < cat list.txt
./test_bash.sh ./test_bash.sh: line 6: syntax error near unexpected token `list.txt' ./test_bash.sh: line 6: ` done < cat list.txt'
On 23/07/2020 15:37, Jerry Geis wrote:
Thanks, when I change it do the following I get a syntax error
#!/bin/bash # while read LINE do echo $LINE done < cat list.txt
done < list.txt
./test_bash.sh ./test_bash.sh: line 6: syntax error near unexpected token `list.txt' ./test_bash.sh: line 6: ` done < cat list.txt' _______________________________________________ CentOS mailing list CentOS@centos.org https://lists.centos.org/mailman/listinfo/centos
On 23/07/2020 16:37, Jerry Geis wrote:
Thanks, when I change it do the following I get a syntax error
#!/bin/bash # while read LINE do echo $LINE done < cat list.txt
You don't use "cat" here; it's not needed at all. You write:
done < list.txt
This tells the shell to redirect the stdin of the while loop from the file "list.txt".
People in the unix world have made a mess of code everywhere by superfluously using "cat". In the old usenet days, anyone who posted shell code with unnecessary use of cat used to be awarded a prize (and it was not something to be proud of, but to be embarrassed about).
"cat" is short for "concatenate", and for that purpose, it is perfect. When you want to take two or more sources of data, and combine them, then cat is the perfect tool, eg:
cat file1 file2 file3 > combined-file
But for most other tasks, if you're using "cat", then you're almost certainly misusing it. For example, people who do:
cat file | grep something
This makes the shell fork and run cat, and then the shell has to setup a pipe to pass the data to grep. Too much overhead. They don't know that they can just do:
grep something file
and let the grep command read the file itself.
Sorry - I see it now "remove the cat".
Thanks "All" for the suggestions. I wasnt aware of the method to avoid the cut command.
Jerry
On Thu, 2020-07-23 at 10:49 -0400, Jerry Geis wrote:
Sorry - I see it now "remove the cat".
Thanks "All" for the suggestions. I wasnt aware of the method to avoid the cut command.
Here's a few "historical" observations on this thread.
1) Your original script looks like you were trying to write to the syntax of the old Bourne ( sometimes called "boring" ) shell. In the olden days of Unix in the 20th century, that was the ONE shell you could reliably expect to be present on the target machine.
2) You are now using Bash ( Bourne-Again SHell ) which is obviously an evolutionary development and is much more capable. It has SO much more capabilities that ( as others have pointed out ) it can do many things with internal functions that used to require other tools ( "cat", "expr", others ) to accomplish.
3) You write scripts in a similar fashion to the way I do it. Plenty of whoopsies and typos along the way to debug. Since I'm now an old geezer from the prehistoric times of Unix, I still stick to the old thumb rule "The man page is your friend" that some people seem to be forgetting these days.
Just my $0.02 (US) worth.
Jerry _______________________________________________ CentOS mailing list CentOS@centos.org https://lists.centos.org/mailman/listinfo/centos
On Thu, Jul 23, 2020 at 4:25 PM Anand Buddhdev anandb@ripe.net wrote:
On 23/07/2020 15:46, Jerry Geis wrote:
Hi Jerry,
See below, inline, for some comments.
while read -r LINE do NODENAME=` echo $LINE | cut -f 1 -d ','`
NODENAME=$(cut -d, -f1 <<< $LINE)
Notes: use $( instead of backticks. There's no need to quote the comma. Write less and write concisely.
IP=` echo $LINE | cut -f 2 -d ','`
IP=$(cut -d, -f2 <<< $LINE)
names[index]="$NODENAME" ip[index]="$IP"
I would add these considerations: 1) -r means to not consider \ character as an escape character so possibly is not important to use it in your scenario 2) read support multiple variables parsing 3) read word separation (default space) can be modified using IFS (internal field separator)
So I would change the script this way, together with other considerations
#!/bin/bash # IFS=','
index=0 total=0 names=() ip=() #while read -r LINE while read NODENAME IP do #NODENAME=$(echo $LINE | cut -f 1 -d ',') #IP=$(echo $LINE | cut -f 2 -d ',') names[$((index++))]="$NODENAME" ip[$((index++))]="$IP" ((total)) done < /tmp/list.txt
to verify you can add something like:
for i in ${names[@]} ${ip[@]} do echo $i done
HIH, Gianluca
Hi,
Some remarks: - just try « expr ${VAR} + 1 » (with blanc between car) - use simple redirection (« < ») with a simple reference to file (« done < list.txt ») - use « ${VAR} » to manage variables - you can use numeric notation to increment VAR (p.e. « total=$(( ${total} + 1 )) »)
An other way to do that: AWK.
Regards
Le 23 juil. 2020 à 15:46, Jerry Geis jerry.geis@gmail.com a écrit :
I have a simple script: #!/bin/bash # index=0 total=0 names=() ip=() while read -r LINE do NODENAME=` echo $LINE | cut -f 1 -d ','` IP=` echo $LINE | cut -f 2 -d ','` names[index]="$NODENAME" ip[index]="$IP" index=`expr index+1` total=`expr total+1` done <<< $(cat list.txt)
simple file: more list.txt name1,ip1 name2,ip2 name3,ip3
output when running: sh -x ./test_bash.sh
- index=0
- total=0
- names=()
- ip=()
++ cat list.txt
- read -r LINE
++ echo name1,ip1 name2,ip2 name3,ip3 ++ cut -f 1 -d ,
- NODENAME=name1
++ echo name1,ip1 name2,ip2 name3,ip3 ++ cut -f 2 -d ,
- IP='ip1 name2'
- names[index]=name1
- ip[index]='ip1 name2'
++ expr index+1
- index=index+1
++ expr total+1
- total=total+1
- read -r LINE
- echo name1
name1
Question is why is it not reading one line at a time ? All I get is the first one. I'm just trying to build the array of the items in the file and then list them at this point.
Thanks
Jerry _______________________________________________ CentOS mailing list CentOS@centos.org https://lists.centos.org/mailman/listinfo/centos
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On 23/07/2020 15:46, Jerry Geis wrote:
Hi Jerry,
You can do even better:
index=0 total=0 names=() ip=()
IFS=,
while read -r NODENAME IP do names[$index]="$NODENAME" ip[$((index++))]="$IP" ((total++)) done < list.txt
In this example, you set the input field separator (IFS) to the comma, so that the shell does the word splitting for you, and then allow the "read" call to assign to both variables in a single call. Now you don't need any "cut" calls. In fact, this example avoids forks completely, by just using native features of bash.
For small inputs, it doesn't matter, but if you were processing a large file, and your script was forking for each call to "cut" and creating a new process, you would incur a horrible amount of overhead for no reason.
Regards, Anand
I have a simple script: #!/bin/bash # index=0 total=0 names=() ip=() while read -r LINE do NODENAME=` echo $LINE | cut -f 1 -d ','` IP=` echo $LINE | cut -f 2 -d ','` names[index]="$NODENAME" ip[index]="$IP" index=`expr index+1` total=`expr total+1` done <<< $(cat list.txt)
simple file: more list.txt name1,ip1 name2,ip2 name3,ip3
output when running: sh -x ./test_bash.sh
- index=0
- total=0
- names=()
- ip=()
++ cat list.txt
- read -r LINE
++ echo name1,ip1 name2,ip2 name3,ip3 ++ cut -f 1 -d ,
- NODENAME=name1
++ echo name1,ip1 name2,ip2 name3,ip3 ++ cut -f 2 -d ,
- IP='ip1 name2'
- names[index]=name1
- ip[index]='ip1 name2'
++ expr index+1
- index=index+1
++ expr total+1
- total=total+1
- read -r LINE
- echo name1
name1
Question is why is it not reading one line at a time ? All I get is the first one. I'm just trying to build the array of the items in the file and then list them at this point.
Thanks
Jerry _______________________________________________ CentOS mailing list CentOS@centos.org https://lists.centos.org/mailman/listinfo/centos
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Anand Buddhdev -
Gianluca Cecchi -
Giles Coochey -
Jerry Geis -
Pierre Malard -
Ron Loftin