[OpenWrt-Devel] [PATCH] mvebu: Replace backticks by $(...)

[Jeff Kletsky]

On 7/24/19 11:05 AM, Rosen Penev wrote:
> On Wed, Jul 24, 2019 at 10:48 AM Adrian Schmutzler
> <mail at adrianschmutzler.de> wrote:
>> Hi,
>>
>>> -----Original Message-----
>>> From: Rosen Penev [mailto:rosenp at gmail.com]
>>> Sent: Mittwoch, 24. Juli 2019 18:54
>>> To: Adrian Schmutzler <freifunk at adrianschmutzler.de>
>>> Cc: OpenWrt Development List <openwrt-devel at lists.openwrt.org>
>>> Subject: Re: [OpenWrt-Devel] [PATCH] mvebu: Replace backticks by $(...)
>>>
>>> On Wed, Jul 24, 2019 at 6:34 AM Adrian Schmutzler
>>> <freifunk at adrianschmutzler.de> wrote:
>>>> Signed-off-by: Adrian Schmutzler <freifunk at adrianschmutzler.de>
>>>> ---
>>>>   target/linux/mvebu/base-files/lib/upgrade/linksys.sh | 2 +-
>>>>   target/linux/mvebu/base-files/sbin/fan_ctrl.sh       | 6 +++---
>>>>   2 files changed, 4 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/target/linux/mvebu/base-files/lib/upgrade/linksys.sh
>>> b/target/linux/mvebu/base-files/lib/upgrade/linksys.sh
>>>> index 3f45d6cac5..ddf24836bc 100644
>>>> --- a/target/linux/mvebu/base-files/lib/upgrade/linksys.sh
>>>> +++ b/target/linux/mvebu/base-files/lib/upgrade/linksys.sh
>>>> @@ -6,7 +6,7 @@ linksys_get_target_firmware() {
>>>>
>>>>          local cur_boot_part mtd_ubi0
>>>>
>>>> -       cur_boot_part=`/usr/sbin/fw_printenv -n boot_part`
>>>> +       cur_boot_part=$(/usr/sbin/fw_printenv -n boot_part)
>>>>          if [ -z "${cur_boot_part}" ] ; then
>>>>                  mtd_ubi0=$(cat /sys/devices/virtual/ubi/ubi0/mtd_num)
>>>>                  case $(egrep ^mtd${mtd_ubi0}: /proc/mtd | cut -d '"' -f 2) in
>>> egrep is deprecated as well. I'm assuming you're running these through
>>> shellcheck.
>> I indeed got this hint from shellcheck, suggesting "grep -E" as replacement.
>> However, I'm not familiar with the old egrep.
>> So, I was not sure whether I really can replace it without side-effects, and since I cannot test on this target, I decided against changing that.
>>
>> If you tell me it's okay, I can include it in a v2.
> egrep is equivalent to grep -E. I have never seen any fallout from
> changing this.

[...]

The one place that I know it is critical to use `grep -E` over `egrep` 
is during stage2 of sysupgrade, when `grep` is typically available and 
`egrep` is often not.

switch_to_ramfs() {
         for binary in \
                 /bin/busybox /bin/ash /bin/sh /bin/mount /bin/umount    \
                 pivot_root mount_root reboot sync kill sleep            \
                 md5sum hexdump cat zcat bzcat dd tar                    \
                 ls basename find cp mv rm mkdir rmdir mknod touch chmod \
                 '[' printf wc grep awk sed cut                          \
                 mtd partx losetup mkfs.ext4                             \
                 ubiupdatevol ubiattach ubiblock ubiformat               \
                 ubidetach ubirsvol ubirmvol ubimkvol                    \
                 snapshot snapshot_tool                                  \
                 $RAMFS_COPY_BIN
[...]


As I've had my hands in `linksys.sh` recently (commit b3770eaca3), I can 
say that the primary reason I didn't change it in that file then was to 
keep the large number of changes somewhat more understandable.


Jeff





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