How to obtain the content of a variable in bash
I have a config file with this content:
config_scrm.sh
CDT_TRIGGER='69'
SR_TRIGGER='165'
In the main script I need to insert the content of CDT_TRIGGER (which is 69) in a variable called TRIGGER. The only thing I have to know I should get that exact variable content is another (local) variable called ELM='CDT'
So, in the main script, I execute:
main.sh
#!/bin/bash
source config_scrm.sh
(some calculations to obtain the value of variable ELM)
ELM='CDT'
I need TRIGGER to be 69.
If ELM='SR', I would need TRIGGER to be 165. And so on, there are way more values than showed in this excerpt.
What is not working:
MYSTRING='_TRIGGER'
TRIGGER=${$ELM$MYSTRING}
or
TRIGGER=`echo "$ELM$MYSTRING"`
or
TRIGGER=`$(echo "$ELM$MYSTRING")`
linux bash environment-variables
asked Jan 14 at 9:06
UxioUxio
153
add a comment |
I have a config file with this content:
config_scrm.sh
CDT_TRIGGER='69'
SR_TRIGGER='165'
In the main script I need to insert the content of CDT_TRIGGER (which is 69) in a variable called TRIGGER. The only thing I have to know I should get that exact variable content is another (local) variable called ELM='CDT'
So, in the main script, I execute:
main.sh
#!/bin/bash
source config_scrm.sh
(some calculations to obtain the value of variable ELM)
ELM='CDT'
I need TRIGGER to be 69.
If ELM='SR', I would need TRIGGER to be 165. And so on, there are way more values than showed in this excerpt.
What is not working:
MYSTRING='_TRIGGER'
TRIGGER=${$ELM$MYSTRING}
or
TRIGGER=`echo "$ELM$MYSTRING"`
or
TRIGGER=`$(echo "$ELM$MYSTRING")`
linux bash environment-variables
asked Jan 14 at 9:06
UxioUxio
153
add a comment |
I have a config file with this content:
config_scrm.sh
CDT_TRIGGER='69'
SR_TRIGGER='165'
In the main script I need to insert the content of CDT_TRIGGER (which is 69) in a variable called TRIGGER. The only thing I have to know I should get that exact variable content is another (local) variable called ELM='CDT'
So, in the main script, I execute:
main.sh
#!/bin/bash
source config_scrm.sh
(some calculations to obtain the value of variable ELM)
ELM='CDT'
I need TRIGGER to be 69.
If ELM='SR', I would need TRIGGER to be 165. And so on, there are way more values than showed in this excerpt.
What is not working:
MYSTRING='_TRIGGER'
TRIGGER=${$ELM$MYSTRING}
or
TRIGGER=`echo "$ELM$MYSTRING"`
or
TRIGGER=`$(echo "$ELM$MYSTRING")`
linux bash environment-variables
asked Jan 14 at 9:06
UxioUxio
153
I have a config file with this content:
config_scrm.sh
CDT_TRIGGER='69'
SR_TRIGGER='165'
In the main script I need to insert the content of CDT_TRIGGER (which is 69) in a variable called TRIGGER. The only thing I have to know I should get that exact variable content is another (local) variable called ELM='CDT'
So, in the main script, I execute:
main.sh
#!/bin/bash
source config_scrm.sh
(some calculations to obtain the value of variable ELM)
ELM='CDT'
I need TRIGGER to be 69.
If ELM='SR', I would need TRIGGER to be 165. And so on, there are way more values than showed in this excerpt.
What is not working:
MYSTRING='_TRIGGER'
TRIGGER=${$ELM$MYSTRING}
or
TRIGGER=`echo "$ELM$MYSTRING"`
or
TRIGGER=`$(echo "$ELM$MYSTRING")`
linux bash environment-variables
linux bash environment-variables
asked Jan 14 at 9:06
UxioUxio
153
asked Jan 14 at 9:06
UxioUxio
153
asked Jan 14 at 9:06
UxioUxio
153
asked Jan 14 at 9:06
UxioUxio
153
asked Jan 14 at 9:06
UxioUxio
153
153
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
Although $ELM$MYSTRING expands to the name you want, TRIGGER=${$ELM$MYSTRING} doesn't work because here you need parameter expansion to occur twice: "inner" variables first, then the "outer" one.
Your tries with command substitution would make little more sense if you actually used the "outer" $ to try to trigger additional parameter expansion; but even then they would fail for similar reason as the above.
Well, you can have parameter expansion in two separate steps. You need eval for this:
eval 'TRIGGER=$'"$ELM$MYSTRING"
At first the variables within "" are expanded normally, everything within '' is left intact. Then eval performs additional parsing of the resulting string which is now exactly TRIGGER=$CDT_TRIGGER. The solution is portable, although you should be careful with eval. Please see Why should eval be avoided in Bash, and what should I use instead?
In Bash there's a safer (yet not portable) way to do what you want:
wholename=$ELM$MYSTRING # we need this in a single variable
TRIGGER=${!wholename}
Side note: consider lowercase names for your variables.
answered Jan 14 at 10:09
Kamil MaciorowskiKamil Maciorowski
26.3k155680
Since the ${!wholename} version is working perfectly, I'll stick to it. Regards.
– Uxio
Jan 14 at 12:57
add a comment |
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1 Answer
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1 Answer
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active
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Although $ELM$MYSTRING expands to the name you want, TRIGGER=${$ELM$MYSTRING} doesn't work because here you need parameter expansion to occur twice: "inner" variables first, then the "outer" one.
Your tries with command substitution would make little more sense if you actually used the "outer" $ to try to trigger additional parameter expansion; but even then they would fail for similar reason as the above.
Well, you can have parameter expansion in two separate steps. You need eval for this:
eval 'TRIGGER=$'"$ELM$MYSTRING"
At first the variables within "" are expanded normally, everything within '' is left intact. Then eval performs additional parsing of the resulting string which is now exactly TRIGGER=$CDT_TRIGGER. The solution is portable, although you should be careful with eval. Please see Why should eval be avoided in Bash, and what should I use instead?
In Bash there's a safer (yet not portable) way to do what you want:
wholename=$ELM$MYSTRING # we need this in a single variable
TRIGGER=${!wholename}
Side note: consider lowercase names for your variables.
answered Jan 14 at 10:09
Kamil MaciorowskiKamil Maciorowski
26.3k155680
Since the ${!wholename} version is working perfectly, I'll stick to it. Regards.
– Uxio
Jan 14 at 12:57
add a comment |
Although $ELM$MYSTRING expands to the name you want, TRIGGER=${$ELM$MYSTRING} doesn't work because here you need parameter expansion to occur twice: "inner" variables first, then the "outer" one.
Your tries with command substitution would make little more sense if you actually used the "outer" $ to try to trigger additional parameter expansion; but even then they would fail for similar reason as the above.
Well, you can have parameter expansion in two separate steps. You need eval for this:
eval 'TRIGGER=$'"$ELM$MYSTRING"
At first the variables within "" are expanded normally, everything within '' is left intact. Then eval performs additional parsing of the resulting string which is now exactly TRIGGER=$CDT_TRIGGER. The solution is portable, although you should be careful with eval. Please see Why should eval be avoided in Bash, and what should I use instead?
In Bash there's a safer (yet not portable) way to do what you want:
wholename=$ELM$MYSTRING # we need this in a single variable
TRIGGER=${!wholename}
Side note: consider lowercase names for your variables.
answered Jan 14 at 10:09
Kamil MaciorowskiKamil Maciorowski
26.3k155680
Since the ${!wholename} version is working perfectly, I'll stick to it. Regards.
– Uxio
Jan 14 at 12:57
add a comment |
Although $ELM$MYSTRING expands to the name you want, TRIGGER=${$ELM$MYSTRING} doesn't work because here you need parameter expansion to occur twice: "inner" variables first, then the "outer" one.
Your tries with command substitution would make little more sense if you actually used the "outer" $ to try to trigger additional parameter expansion; but even then they would fail for similar reason as the above.
Well, you can have parameter expansion in two separate steps. You need eval for this:
eval 'TRIGGER=$'"$ELM$MYSTRING"
At first the variables within "" are expanded normally, everything within '' is left intact. Then eval performs additional parsing of the resulting string which is now exactly TRIGGER=$CDT_TRIGGER. The solution is portable, although you should be careful with eval. Please see Why should eval be avoided in Bash, and what should I use instead?
In Bash there's a safer (yet not portable) way to do what you want:
wholename=$ELM$MYSTRING # we need this in a single variable
TRIGGER=${!wholename}
Side note: consider lowercase names for your variables.
answered Jan 14 at 10:09
Kamil MaciorowskiKamil Maciorowski
26.3k155680
Although $ELM$MYSTRING expands to the name you want, TRIGGER=${$ELM$MYSTRING} doesn't work because here you need parameter expansion to occur twice: "inner" variables first, then the "outer" one.
Your tries with command substitution would make little more sense if you actually used the "outer" $ to try to trigger additional parameter expansion; but even then they would fail for similar reason as the above.
Well, you can have parameter expansion in two separate steps. You need eval for this:
eval 'TRIGGER=$'"$ELM$MYSTRING"
At first the variables within "" are expanded normally, everything within '' is left intact. Then eval performs additional parsing of the resulting string which is now exactly TRIGGER=$CDT_TRIGGER. The solution is portable, although you should be careful with eval. Please see Why should eval be avoided in Bash, and what should I use instead?
In Bash there's a safer (yet not portable) way to do what you want:
wholename=$ELM$MYSTRING # we need this in a single variable
TRIGGER=${!wholename}
Side note: consider lowercase names for your variables.
answered Jan 14 at 10:09
Kamil MaciorowskiKamil Maciorowski
26.3k155680
answered Jan 14 at 10:09
Kamil MaciorowskiKamil Maciorowski
26.3k155680
answered Jan 14 at 10:09
Kamil MaciorowskiKamil Maciorowski
26.3k155680
answered Jan 14 at 10:09
Kamil MaciorowskiKamil Maciorowski
26.3k155680
26.3k155680
Since the ${!wholename} version is working perfectly, I'll stick to it. Regards.
– Uxio
Jan 14 at 12:57
add a comment |
Since the ${!wholename} version is working perfectly, I'll stick to it. Regards.
– Uxio
Jan 14 at 12:57
Since the ${!wholename} version is working perfectly, I'll stick to it. Regards.
– Uxio
Jan 14 at 12:57
Since the ${!wholename} version is working perfectly, I'll stick to it. Regards.
– Uxio
Jan 14 at 12:57
add a comment |
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