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I am with CentOS 7 and I want to bind an alias to launch PostgreSQL shell(psql). I defined this alias and append it in /etc/profile.d/alias:

alias psql-local="read -p \"PSQL: enter the DB to connect: \" db ; sudo -i -u postgres psql --dbname $db"

It is executable by root.

And, I login as root, and run alias, I get:

alias psql-local='read -p "PSQL: enter the DB to connect: " db ; sudo -i -u postgres psql --dbname '

Note here $db at the end is empty.

Then I run psql-local, but I get error:

[root@lucas_vm ~]
> psql-local
PSQL: enter the DB to connect: jfps
psql: option '--dbname' requires an argument
Try "psql --help" for more information.

Then I enter /etc/profile.d/, and run alias.sh manually, then suddenly I can use this alias:

[root@lucas_vm /etc/profile.d]
> . alias.sh
[root@lucas_vm /etc/profile.d]
> psql-local
PSQL: enter the DB to connect: jfps
psql (10.5)
Type "help" for help.

jfps=#

If I exit psql and run alias again, I see this line changed:

alias psql-local='read -p "PSQL: enter the DB to connect: " db ; sudo -i -u postgres psql --dbname jfps'

Note $db is changed to jfps.

Then, I try to access another database, and it works again.

But, when I exit and alias, I see the --dbname jfps, not the name of second database. When I echo $db, it, instead, is the name of the second db.

Why?

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1 Answer 1

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Because you're using double-quotes ("..."), the $db variable will be expanded when you define the alias, not when it's used. Try this instead:

alias psql-local='read -p "PSQL: enter the DB to connect: " db ; sudo -i -u postgres psql --dbname "$db"'
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  • Um.. it improves: when login and alias, I see: alias psql-local='read -p \"PSQL: enter the DB to connect: \" db ; sudo -i -u postgres psql --dbname "$db"', but when I use it, I see error: > psql-local \n "PSQL:jfps \n -bash: read: `connect:': not a valid identifier \n psql: option '--dbname' requires an argument \n Try "psql --help" for more information. Seems the script is truncated due to single quotes. Commented Feb 1, 2019 at 9:33
  • I also tried: 1) single quote $db; 2) escape " and double quote $db 3) double quote $db without escaping. But no avail. Commented Feb 1, 2019 at 9:40
  • try prepending a printf "{%s} " before sudo ... and tell me the output you're getting. Commented Feb 1, 2019 at 9:42
  • OK so I changed back to your solution (single quote all) and add what you said, and I got same error as before, but with extra {}. Seems empty {%s}. Commented Feb 1, 2019 at 9:46
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    The best thing is to use set -x and the printf "{%s} " ... trick when in doubt. Anyways, variables ($x) and other $ expansions are performed inside double quotes ("...") but not inside single quotes ('...'). Commented Feb 1, 2019 at 10:03

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