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bash aliases do not expand even with shopt expand_aliases

In Bash, when to alias, when to script, and when to write a function?bash: dynamic environment controlUnable to get back to bash prompt after strange commandWhy does my Cygwin Bash always read from terminal when I try to execute an external command?Bash isn't reading (source) .bashrc in AIXWhich of the following shell operations are performed inside the function body when running a function definition and when calling a function?“a word that is identical to an alias being expanded is not expanded a second time”how to let sudo fork bash instead of sh?what shell is used to run a scriptWhy is an alias in a script being sourced in an interactive bash process not expanded?

2

I want to run an alias inside a bash -c construct.

The bash manual says:

Aliases are not expanded when the shell is not interactive, unless the expand_aliases shell option is set using shopt

In this example, why is the alias hi not found when setting expand_aliases explicitly?

% bash -O expand_aliases -c "alias hi='echo hello'; alias; shopt expand_aliases; hi"

alias hi='echo hello'

expand_aliases  on

bash: hi: command not found

I'm running GNU bash, version 5.0.0(1)-release (x86_64-pc-linux-gnu).

Context: I want to be able to run an alias at idle priority, eg a script containing:

#!/bin/bash

exec chrt -i 0 nice -n 19 ionice -c 3 bash -c ". ~/.config/bash/aliases; shopt -s expand_aliases; $(shell-quote "$@")"

I want to avoid using bash -i as I don't want my .bashrc to be read.

bash alias

share|improve this question

edited 1 hour ago

Tom Hale

asked 1 hour ago

Tom HaleTom Hale

7,11333797

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  The paragraph right after the quoted statement from the Bash manual seems to cover this: '...Aliases are expanded when a command is read, not when it is executed. Therefore, an alias definition appearing on the same line as another command does not take effect until the next line of input is read. The commands following the alias definition on that line are not affected by the new alias....'
  
  – Haxiel
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Haxiel, you really should write things like that as answers.
  
  – ilkkachu
  59 mins ago
  

  
  
  
  

add a comment | 

2

I want to run an alias inside a bash -c construct.

The bash manual says:

Aliases are not expanded when the shell is not interactive, unless the expand_aliases shell option is set using shopt

In this example, why is the alias hi not found when setting expand_aliases explicitly?

% bash -O expand_aliases -c "alias hi='echo hello'; alias; shopt expand_aliases; hi"

alias hi='echo hello'

expand_aliases  on

bash: hi: command not found

I'm running GNU bash, version 5.0.0(1)-release (x86_64-pc-linux-gnu).

Context: I want to be able to run an alias at idle priority, eg a script containing:

#!/bin/bash

exec chrt -i 0 nice -n 19 ionice -c 3 bash -c ". ~/.config/bash/aliases; shopt -s expand_aliases; $(shell-quote "$@")"

I want to avoid using bash -i as I don't want my .bashrc to be read.

bash alias

share|improve this question

edited 1 hour ago

Tom Hale

asked 1 hour ago

Tom HaleTom Hale

7,11333797

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  The paragraph right after the quoted statement from the Bash manual seems to cover this: '...Aliases are expanded when a command is read, not when it is executed. Therefore, an alias definition appearing on the same line as another command does not take effect until the next line of input is read. The commands following the alias definition on that line are not affected by the new alias....'
  
  – Haxiel
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Haxiel, you really should write things like that as answers.
  
  – ilkkachu
  59 mins ago
  

  
  
  
  

add a comment | 

I want to run an alias inside a bash -c construct.

The bash manual says:

Aliases are not expanded when the shell is not interactive, unless the expand_aliases shell option is set using shopt

In this example, why is the alias hi not found when setting expand_aliases explicitly?

% bash -O expand_aliases -c "alias hi='echo hello'; alias; shopt expand_aliases; hi"

alias hi='echo hello'

expand_aliases  on

bash: hi: command not found

I'm running GNU bash, version 5.0.0(1)-release (x86_64-pc-linux-gnu).

Context: I want to be able to run an alias at idle priority, eg a script containing:

#!/bin/bash

exec chrt -i 0 nice -n 19 ionice -c 3 bash -c ". ~/.config/bash/aliases; shopt -s expand_aliases; $(shell-quote "$@")"

I want to avoid using bash -i as I don't want my .bashrc to be read.

bash alias

share|improve this question

edited 1 hour ago

Tom Hale

asked 1 hour ago

Tom HaleTom Hale

7,11333797

% bash -O expand_aliases -c "alias hi='echo hello'; alias; shopt expand_aliases; hi"

alias hi='echo hello'

expand_aliases  on

bash: hi: command not found

#!/bin/bash

exec chrt -i 0 nice -n 19 ionice -c 3 bash -c ". ~/.config/bash/aliases; shopt -s expand_aliases; $(shell-quote "$@")"

share|improve this question

edited 1 hour ago

Tom Hale

asked 1 hour ago

Tom HaleTom Hale

7,11333797

share|improve this question

edited 1 hour ago

Tom Hale

asked 1 hour ago

Tom HaleTom Hale

7,11333797

asked 1 hour ago

Tom HaleTom Hale

7,11333797

asked 1 hour ago

Tom HaleTom Hale

7,11333797

2 Answers
2

active

oldest

votes

5

It doesn't seem work if you set the alias on the same line as it's used. Probably something to do with how aliases are expanded really early in the command line processing, before the actual parsing stage. On an interactive shell:

$ alias foo

bash: alias: foo: not found

$ alias foo='echo foo'; foo         # 2 

bash: foo: command not found

$ alias foo='echo bar'; foo         # 3

foo

$ foo

bar

Note how the alias used is one line late: on the second command it doesn't find the alias just set, and on the third command it uses the one that was previously set.

So, it works if we put a newline within the -c string:

$ bash -c $'shopt -s expand_aliases; alias foo="echo foo";n foo'

foo

(You could also use bash -O expand_aliases -c ... instead of using shopt within the script, not that it helps with the newline.)

Alternatively, you could use a shell function instead of an alias, they're much better in other ways, too:

$ bash -c 'foo() { echo foo; }; foo'

foo

share|improve this answer

answered 1 hour ago

ilkkachuilkkachu

59.6k894168

add a comment | 

0

Turning my comment into an answer, as suggested by ilkkachu.

The Bash manual (linked to in the question) does provide an explanation of how the aliases are handled when there is an alias definition and a command on the same line.

Quote (slightly formatted for clarity):

The rules concerning the definition and use of aliases are somewhat
confusing. Bash always reads at least one complete line of input, and
all lines that make up a compound command, before executing any of the
commands on that line or the compound command.

Aliases are expanded when a command is read, not when it is executed.
Therefore, an alias definition appearing on the same line as another
command does not take effect until the next line of input is read. The
commands following the alias definition on that line are not affected
by the new alias.

This behavior is also an issue when functions are executed. Aliases
are expanded when a function definition is read, not when the function
is executed, because a function definition is itself a command. As a
consequence, aliases defined in a function are not available until
after that function is executed.

To be safe, always put alias definitions on a separate line, and do
not use alias in compound commands.

ilkkachu's answer provides multiple possible solutions to this problem.

share|improve this answer

answered 26 mins ago

HaxielHaxiel

2,7851916

add a comment | 

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5

It doesn't seem work if you set the alias on the same line as it's used. Probably something to do with how aliases are expanded really early in the command line processing, before the actual parsing stage. On an interactive shell:

$ alias foo

bash: alias: foo: not found

$ alias foo='echo foo'; foo         # 2 

bash: foo: command not found

$ alias foo='echo bar'; foo         # 3

foo

$ foo

bar

Note how the alias used is one line late: on the second command it doesn't find the alias just set, and on the third command it uses the one that was previously set.

So, it works if we put a newline within the -c string:

$ bash -c $'shopt -s expand_aliases; alias foo="echo foo";n foo'

foo

(You could also use bash -O expand_aliases -c ... instead of using shopt within the script, not that it helps with the newline.)

Alternatively, you could use a shell function instead of an alias, they're much better in other ways, too:

$ bash -c 'foo() { echo foo; }; foo'

foo

share|improve this answer

answered 1 hour ago

ilkkachuilkkachu

59.6k894168

add a comment | 

5

It doesn't seem work if you set the alias on the same line as it's used. Probably something to do with how aliases are expanded really early in the command line processing, before the actual parsing stage. On an interactive shell:

$ alias foo

bash: alias: foo: not found

$ alias foo='echo foo'; foo         # 2 

bash: foo: command not found

$ alias foo='echo bar'; foo         # 3

foo

$ foo

bar

Note how the alias used is one line late: on the second command it doesn't find the alias just set, and on the third command it uses the one that was previously set.

So, it works if we put a newline within the -c string:

$ bash -c $'shopt -s expand_aliases; alias foo="echo foo";n foo'

foo

(You could also use bash -O expand_aliases -c ... instead of using shopt within the script, not that it helps with the newline.)

Alternatively, you could use a shell function instead of an alias, they're much better in other ways, too:

$ bash -c 'foo() { echo foo; }; foo'

foo

share|improve this answer

answered 1 hour ago

ilkkachuilkkachu

59.6k894168

add a comment | 

It doesn't seem work if you set the alias on the same line as it's used. Probably something to do with how aliases are expanded really early in the command line processing, before the actual parsing stage. On an interactive shell:

$ alias foo

bash: alias: foo: not found

$ alias foo='echo foo'; foo         # 2 

bash: foo: command not found

$ alias foo='echo bar'; foo         # 3

foo

$ foo

bar

Note how the alias used is one line late: on the second command it doesn't find the alias just set, and on the third command it uses the one that was previously set.

So, it works if we put a newline within the -c string:

$ bash -c $'shopt -s expand_aliases; alias foo="echo foo";n foo'

foo

(You could also use bash -O expand_aliases -c ... instead of using shopt within the script, not that it helps with the newline.)

Alternatively, you could use a shell function instead of an alias, they're much better in other ways, too:

$ bash -c 'foo() { echo foo; }; foo'

foo

share|improve this answer

answered 1 hour ago

ilkkachuilkkachu

59.6k894168

$ alias foo

bash: alias: foo: not found

$ alias foo='echo foo'; foo         # 2 

bash: foo: command not found

$ alias foo='echo bar'; foo         # 3

foo

$ foo

bar

$ bash -c $'shopt -s expand_aliases; alias foo="echo foo";n foo'

foo

$ bash -c 'foo() { echo foo; }; foo'

foo

share|improve this answer

answered 1 hour ago

ilkkachuilkkachu

59.6k894168

answered 1 hour ago

ilkkachuilkkachu

59.6k894168

answered 1 hour ago

ilkkachuilkkachu

59.6k894168

0

Turning my comment into an answer, as suggested by ilkkachu.

The Bash manual (linked to in the question) does provide an explanation of how the aliases are handled when there is an alias definition and a command on the same line.

Quote (slightly formatted for clarity):

The rules concerning the definition and use of aliases are somewhat
confusing. Bash always reads at least one complete line of input, and
all lines that make up a compound command, before executing any of the
commands on that line or the compound command.

Aliases are expanded when a command is read, not when it is executed.
Therefore, an alias definition appearing on the same line as another
command does not take effect until the next line of input is read. The
commands following the alias definition on that line are not affected
by the new alias.

This behavior is also an issue when functions are executed. Aliases
are expanded when a function definition is read, not when the function
is executed, because a function definition is itself a command. As a
consequence, aliases defined in a function are not available until
after that function is executed.

To be safe, always put alias definitions on a separate line, and do
not use alias in compound commands.

ilkkachu's answer provides multiple possible solutions to this problem.

share|improve this answer

answered 26 mins ago

HaxielHaxiel

2,7851916

add a comment | 

0

Turning my comment into an answer, as suggested by ilkkachu.

The Bash manual (linked to in the question) does provide an explanation of how the aliases are handled when there is an alias definition and a command on the same line.

Quote (slightly formatted for clarity):

The rules concerning the definition and use of aliases are somewhat
confusing. Bash always reads at least one complete line of input, and
all lines that make up a compound command, before executing any of the
commands on that line or the compound command.

Aliases are expanded when a command is read, not when it is executed.
Therefore, an alias definition appearing on the same line as another
command does not take effect until the next line of input is read. The
commands following the alias definition on that line are not affected
by the new alias.

This behavior is also an issue when functions are executed. Aliases
are expanded when a function definition is read, not when the function
is executed, because a function definition is itself a command. As a
consequence, aliases defined in a function are not available until
after that function is executed.

To be safe, always put alias definitions on a separate line, and do
not use alias in compound commands.

ilkkachu's answer provides multiple possible solutions to this problem.

share|improve this answer

answered 26 mins ago

HaxielHaxiel

2,7851916

add a comment | 

Turning my comment into an answer, as suggested by ilkkachu.

The Bash manual (linked to in the question) does provide an explanation of how the aliases are handled when there is an alias definition and a command on the same line.

Quote (slightly formatted for clarity):

The rules concerning the definition and use of aliases are somewhat
confusing. Bash always reads at least one complete line of input, and
all lines that make up a compound command, before executing any of the
commands on that line or the compound command.

Aliases are expanded when a command is read, not when it is executed.
Therefore, an alias definition appearing on the same line as another
command does not take effect until the next line of input is read. The
commands following the alias definition on that line are not affected
by the new alias.

This behavior is also an issue when functions are executed. Aliases
are expanded when a function definition is read, not when the function
is executed, because a function definition is itself a command. As a
consequence, aliases defined in a function are not available until
after that function is executed.

To be safe, always put alias definitions on a separate line, and do
not use alias in compound commands.

ilkkachu's answer provides multiple possible solutions to this problem.

share|improve this answer

answered 26 mins ago

HaxielHaxiel

2,7851916

share|improve this answer

answered 26 mins ago

HaxielHaxiel

2,7851916

answered 26 mins ago

HaxielHaxiel

2,7851916

answered 26 mins ago

HaxielHaxiel

2,7851916