Source version.txt to get version information

This guards against possible quotes.

content/docs/latest/installing/cloud/azure.md

@@ -558,7 +558,7 @@ resource_group_location = "westeurope"
 You can resolve the latest Flatcar Stable version with this shell command:
 
 ```
-curl -sSfL https://stable.release.flatcar-linux.net/amd64-usr/current/version.txt | grep -m 1 FLATCAR_VERSION_ID= | cut -d = -f 2
+(source <(curl -sSfL https://stable.release.flatcar-linux.net/amd64-usr/current/version.txt); echo "${FLATCAR_VERSION_ID}")
 ```
 
 The machine name listed in the `machines` variable is used to retrieve the corresponding [Container Linux Config](../../provisioning/config-transpiler/configuration) template from the `cl/` subfolder.

content/docs/latest/installing/cloud/digitalocean.md

@@ -127,7 +127,7 @@ read SSH_KEY_ID
 If not done yet, [create a custom image](https://developers.digitalocean.com/documentation/v2/#create-a-custom-image) from the current Flatcar Container Linux Stable version:
 
 ```shell
-VER=$(curl https://stable.release.flatcar-linux.net/amd64-usr/current/version.txt | grep -m 1 FLATCAR_VERSION_ID= | cut -d = -f 2)
+VER=$(source <(curl https://stable.release.flatcar-linux.net/amd64-usr/current/version.txt); echo "${FLATCAR_VERSION_ID}")
 curl --request POST "https://api.digitalocean.com/v2/images" \
      --header "Content-Type: application/json" \
      --header "Authorization: Bearer $TOKEN" \
@@ -339,7 +339,7 @@ flatcar_stable_version = "x.y.z"
 You can resolve the latest Flatcar Stable version with this shell command:
 
 ```shell
-curl -sSfL https://stable.release.flatcar-linux.net/amd64-usr/current/version.txt | grep -m 1 FLATCAR_VERSION_ID= | cut -d = -f 2
+(source <(curl -sSfL https://stable.release.flatcar-linux.net/amd64-usr/current/version.txt); echo "${FLATCAR_VERSION_ID}")
 ```
 
 The machine name listed in the `machines` variable is used to retrieve the corresponding [Butane Config](https://www.flatcar.org/docs/latest/provisioning/config-transpiler/configuration/).

content/docs/latest/migrating-from-coreos/update-from-container-linux.md

@@ -29,7 +29,7 @@ core@host ~ $ sudo systemctl reboot
 If it fails due to SSL connection issues from outdated certificates, you can also download the update payload of the latest Stable release through plain HTTP and use the `flatcar-update` script instead:
 
 ```shell
-$ VER=$(curl -fsSL --insecure --ssl-no-revoke http://stable.release.flatcar-linux.net/amd64-usr/current/version.txt | grep FLATCAR_VERSION= | cut -d = -f 2)
+$ VER=$(source <(curl -fsSL --insecure --ssl-no-revoke http://stable.release.flatcar-linux.net/amd64-usr/current/version.txt); echo "${FLATCAR_VERSION}")
 $ wget --no-check-certificate "http://update.release.flatcar-linux.net/amd64-usr/$VER/flatcar_production_update.gz"
 $ wget --no-check-certificate http://raw.githubusercontent.com/flatcar/init/flatcar-master/bin/flatcar-update
 $ less flatcar-update # Double check the content of the script

content/docs/latest/reference/developer-guides/sdk-tips-and-tricks.md

@@ -218,7 +218,7 @@ In some cases such a file can pin an exact version of a specific package, which
 Some packages like `coreos-modules` take a long time to build. Use:
 
 ```shell
-./build_packages --getbinpkgver=$(gsutil cat gs://…/boards/amd64-usr/current-master/version.txt |& sed -n 's/^FLATCAR_VERSION=//p')
+./build_packages --getbinpkgver=$(source <(gsutil cat gs://…/boards/amd64-usr/current-master/version.txt); echo "${FLATCAR_VERSION}")
 ```
 
 to use packages from the another build store.

content/docs/latest/setup/releases/switching-channels.md

@@ -89,7 +89,7 @@ $ # In case another channel is set as GROUP, first remove it so that in the futu
 $ sudo sed -i "/GROUP=.*/d" /etc/flatcar/update.conf
 $ # Set the channel you want to jump to:
 $ CHANNEL=beta
-$ VER=$(curl -fsSL "https://$CHANNEL.release.flatcar-linux.net/amd64-usr/current/version.txt" | grep FLATCAR_VERSION= | cut -d = -f 2)
+$ VER=$(source <(curl -fsSL "https://$CHANNEL.release.flatcar-linux.net/amd64-usr/current/version.txt"); echo "${FLATCAR_VERSION}")
 $ sudo flatcar-update --to-version "$VER"
 ```
 

content/docs/latest/setup/releases/update-strategies.md

@@ -189,7 +189,7 @@ The `flatcar-update` tool automatically removes the `SERVER=disabled` line to ap
 
 ```shell
 $ # For example, update to the latest Stable release:
-$ VER=$(curl -fsSL https://stable.release.flatcar-linux.net/amd64-usr/current/version.txt | grep FLATCAR_VERSION= | cut -d = -f 2)
+$ VER=$(source <(curl -fsSL https://stable.release.flatcar-linux.net/amd64-usr/current/version.txt); echo "${FLATCAR_VERSION}")
 $ sudo flatcar-update --to-version $VER
 ```
 
@@ -236,7 +236,7 @@ On the non-airgapped machine (here for amd64, use `ARCH=arm64` for arm64):
 
 ```shell
 ARCH=amd64
-VER=$(curl -fsSL https://stable.release.flatcar-linux.net/${ARCH}-usr/current/version.txt | grep FLATCAR_VERSION= | cut -d = -f 2)
+VER=$(source <(curl -fsSL "https://stable.release.flatcar-linux.net/${ARCH}-usr/current/version.txt"; echo "${FLATCAR_VERSION}")
 echo "$VER"
 # or if you know which version to update to, set it like VER=3033.2.1 (no channel info needed)
 wget "https://update.release.flatcar-linux.net/${ARCH}-usr/${VER}/flatcar_production_update.gz"